Here's Tychus, relatively short hand for now - will touch it up - but feedback/queries welcomed:
Level 1 - press the advantage, gives huge chasing capability, can synergise well with later talents, allows for safer laning/pushing and some kiting (though stutter stepping with tychus is funny as you have to wait for a brief moment for the first attacks to actually register). Cooldown reducing from attacks is okay for survivability but at lvl 1 it's a low payoff choice (how dyou know you need to survive at lvl 1?) the quest isn't great imo.
4 - In the Rhythm 95% of the time, gives huge value the later the game gets and allows you to simply melt their frontline, synergising well with your 13 talent. The bigger they are is good if you're going Odin, or for melting a single tank frontline, attack speed quest feels pointless (barely noticed a difference even when completed), minigun cooldown is ok but the others are just so much better.
7 - Quarterback most of the time, great for securing kills, delaying channels, poking. Relentless is ok too if you need it.
10 - I usually go drill because you want your minigun up in fights. Odin can do huge single target damage and aoe damage which is good for some maps like infernal shrines where your drill won't get as much value on the objective without perfect placement/constant retargeting or against comps where you won't have as much time for minigunning. A well placed drill though deals a lot of subtle damage in a teamfight and is a great zoning/bodyblocking tool (as well as operating as a small damage soak), but its main value is in allowing you to keep using your minigun.
13 - I usually take That's the Stuff, its synergy with In the Rhythm is amazing as lategame you get great self sustain. This also gives you huge 1v1 potential with your grenade + range talent, you can 1v1 pretty much any other assassin/spec/warrior/support if they let you stand still. You can take overkilll range if you're going for Odin, but the heal is still usually better. The damage reduction is pretty good but I'd rather heal than just reduce damage. Look out for Butcher and Kharazim - they can still out 1v1 you. Illidan can be beaten with good timing - proc D as evasion runs out, use Q + W when evasion starts.
16 - Usually I take Titan Grenade just for extra damage (5% of max health is no joke - for say a level 20 muradin of 5769 hp a grenade will do 561 + 288.45 damage) but armor piercing rounds is pretty solid for further frontline melting or against illidan. I tend to use minigun and then overkill in fights (with grenades thrown at their squishies too) and if they have a lot of dive more overkill damage is never bad. If you're paired with heroes that benefit from slows (executioners, lunara etc) the slow on overkill is ok as well.
20 - If you're struggling to secure kills/dying a lot, take Bob and Weave for that lvl 1 synergy, which also works well with Odin. if you're looking to do a lot of damage in siege (aka killing a keep/core) or for defense (such as against a boss/punisher/immortal) and you didn't go Odin take the upgrade to drill and use it to focus said target, but that's situational only. big red button is good as it adds pretty serious aoe damage and a lot of duration to odin. But Sizzlin' Attacks is my go to, it's an extra 1% health damage (almost giant killer value) on top of the existing damage minigun gives, synergises well with 13 and 1 too - with late game In the Rhythm stacks you're looking at dropping insane damage onto their frontline over quite an extended period of time and healing throughout it.
Laning - tychus is solid in lane, overkill and grenade are decent waveclear tools and he isn't massively mana intensive. he has decent hp regen. he can solo lane well enough against similar ranged assassins, but will get firmly rekt by poke sustain like thrall or alarak. he's great to lane against heroes like chen or dehaka (who are good for farming his quest). poke the hero with the grenade and focus the Q on the back minions so you get max damage out of it. If they close to you, you can use W to push them away from you. If chasing, place W just ahead of them - the knockback will bring them closer to you/your team which might be enough to secure the kill.
Fights - tychus is a midrange hero so position him just behind your frontline. You have more hp than most assassins so don't be afraid to be aggressive - with your healing talent you can effectively get onto their squishies and outlast them once the frontline is out of action. Use grenade to poke before fights, and generally to be annoying doing things like dismounting enemy heroes etc throughout the game - with the range, for example, you can get a grenade off over a wall to dismount multiple heroes as they are going to a tribute spawn for example to give your team extra time.
In fights, watch for blinds and turn minigun on at the right time and focus down their frontline. Try to get the one without escape/sustain or shields - dehaka can burrow, tyrael and johanna can shield, but ETC and mura will take a lot of punishment. Use Q on them if they are grouped, and throw grenades into crowds or to pick squishies/fleeing targets. After 10, try placing your drill to block off a potential escape, or in a bush where it is less likely to get focused. Don't forget to retarget it if the initial target dies or moves out of range - the drill may switch to nearby minions. activate odin just as the fight starts and focus your damage on their backline as you have huge range.
After 13 you can bait dives pretty easily with your self sustain. Stand still, let them jump you, and have your team surprise them to save you. After 20 you're lethal to everyone, so don't be afraid of taking some punishment.
You're also one of the best heroes in the game at taking out the DK or Garden Terror with minigun, so if the enemy team has one, make sure you're there defending it. You should avoid getting in the terror/dk unless absolutely necessary. Note that minigun doesn't work on neutral plant terrors, so don't waste it there.
When to pick/how to counter? Tychus fits in well to and against most comps at the moment, but he is best taken against teams with multiple warriors. if they have 1 warrior he works well too though as you can kill it super quick so your team can get onto their backline. he is godly against Cho'Gall and a great pick against ETC, Azmodan, Chen and Diablo in particular. Be careful with Zarya as you can give her energy very quickly if you target her when her shield is up. Johanna can also blind you, stun you and absorb damage with her shields, so be wary of that. If they take a lot of blind to deal with you, you still have a lot of magic damage with overkill and grenade. Be wary about picking him into pick based comps as his single target burst only really takes off after 16, and be cautious about taking him against stun heavy teams, as stunning Tychus is the best way to deal with minigun, since simply leaving his range when he procs it is likely leaving your backline exposed regardless. Tychus can struggle in a team that lacks hard engage and lockdown when competing against a team with good poke and disengage - he ideally needs a target locked down so he can really unload his damage on them. Of course, engaging onto him gives him this opportunity, so hit and run type comps are very effective.