I was able to pick up a copy yesterday here in NYC. Some pictures:
These are the default controls but you can customize them however you want:
The touch screen is used for the map, items and pills/cards.
Here are some screenshots from the game (being played in portable mode):
I never put in a crazy amount of hours into this game. I think Rebirth was the last time I played so I don't know too much about all the items and whatnot but I do know it's an awesome game. Very fun and this was a definite purchase on the Switch.
I agree this seems better as a digital title but a physical release (with a manual!) for a game like this was too good to pass up.
From my 45 min or so playtime in portable mode, I haven't had any slowdown or any issues at all. Runs very smooth and looks great. I can't say how things will be once you get a combination of crazy items but I'm confident it'll be fine.
Playing on the TV is good as well. No complaints with that. Looks fine and runs smooth as well but I see myself spending the majority of my playtime on portable. That screen makes every game look beautiful.
I'm using a solo joy-con just to test it out. Not bad. They have it so that the L button would activate your item. I can see myself accidentally pressing it while playing so that may be the only issue but since you can configure controls, you can fix that. A single joy-con wouldn't be my first choice but that's in general with any game. Feels too cramped for me but it definitely works because of how simple the controls are.
Both joy-cons are how I play. I think the face buttons feel better in terms of shooting. Again, just a personal preference.
In terms of co-op, 2nd played would hit start on their control and choose from 5 different characters. Their faces are what sets them apart and each time you start a new game, there are different faces to choose from. You take 1 heart from the main character. If 2nd player dies, they turn into a big bomb and explode. You can jump right back in and take another heart if you want. If the main character has only 1 heart left, then you get only half a heart.
I can confirm that the only character unlocked from the start is Isaac.
There are daily challenges (which are up and running) and leaderboards for them, which you can sort by Global/Friends/Mine.
Like I said, I don't have too much experience with this game but from the few hours I have played I think it's awesome. Definitely a must buy.