So after a solid day playing this....
Lost Dove is way too common. I think I killed Mom three times with it at least.
Famine on Level 1 AGAIN? *sigh*
Widow on Level 1? *sigh*
Please god, no more Ipecac.
The sacrificial rooms? I can't seem to see a real use for them except for people who like the dead cat...and that just seems like a waste of lives unless you're getting multiple dead cats in one game. It's just kind of a useless room.
The spiked doorways that lead to evil chests rarely seem worth it. You only seem to take damage going one way when you're flying.
I lol'd at the Ankh. Such a fun idea.
There's more than just one secret room per level sometimes, and they seem to disobey the general rule that secret rooms connect to as many other rooms as possible. The Miner's Helmet and X-ray Glasses just got x2 as useful. Not just because you get secret room stuff...but because they're often rooms that have faith.
On that note, the Prayer Card may be one of the best items in the game right now. Used right after you kill a boss but before you go down a level, it guarantees you another heart container. You really can't beat ~3 - 7 extra heart containers. The Book of Revelations still gives it a run for its money though.
The Fortune Telling Machine is funny. I can't tell if there's any effect from the message or if it's just being cute. I don't use it a lot because I'm trying to sort out what trinkets do and swapping them up doesn't help that. But it does seem to like to give out Soul Hearts and Tarot Cards a lot too.
Red Patch is a great trinket (one of the few I've figured out what it does.) Get damage boost the first time you take red heart damage? Yes please.
Puppie's Paw. LULZ.
Curse of the Labyrinth is both a blessing and a curse. Ever sad that levels can go so quickly in BoI? Blessing. Not wanting to spend 20 minutes on one floor? Curse. Loot hungry? Blessing. On Womb 2? Curse.
Screw Devil Begger. He'll take as many as 2 hearts before giving you something something.
Still have no idea what the playing cards do.
Bloody Lust is probably my favorite new item. It really helps compensate for a lack of damage and helps clear rooms much easier. Red Patch + Blood Lust + Any of the Demonic upgrades = Beast.
Haven't tried any of the challenges, but some of the sound fun.
Lastly, a question.
What's the deal with getting to Sheol or Heaven? I've seen the trap door to Sheol once but opened the chest instead (I'm at 9 wins.) I haven't seen the entrance to Heaven yet.
All in all, this was worth $3 and then some. I only wish McMillen wasn't moving on to another game or that this could go open source, because it's still got room to grow.