Downloaded it on my iPhone 4 last night and it runs great. The issue I have with it is the same as with Zen on the iPhone - it's too uncomfortable for me to hold the phone like that. If there was a landscape mode, that might help. Framerate is great, graphics and audio are nice, but I'd prefer to play it on something with buttons (not the 3DS. I hate Zen Pinball on that because of how awful it looks and how small the screen is). If my wife gets an iPad 3, I'll check it out there and possibly also on Vita. I do miss the days when I had time to go to an arcade and play real pinball.
Someone pointed out upthread that there is landscape mode, you just have to rotate the device while you're on the menus, not in-game (like you can do with Zen).
Anyhow I've spent more time with it (and bought all the tables), and I'm feeling a bit better about it now than I was earlier. It's a good selection of tables for launch, particularly Black Hole and Theatre of Magic. (I agree with whoever said Ripley's is way too busy, though.) The table guide is just as good as it was in Williams Collection (Zen sorely needs this). The physics do feel good, although I would almost say they're too fast - having a hard time trapping on a flipper when a ball is coming through a lane, which seems unrealistic.
The game also runs much better on an iPad 1 than Zen does - it's actually playable! As Minsc said, the textures are really muddy, but hopefully that can be addressed.
And as an iOS specific complaint, I get that they're doing a "have you purchased this table yet" check whenever you open a table, but prompting the user to log into their store account every time you open a table is clumsy and borderline dangerous.
Still - quite happy, happy to see more tables coming, and will buy all of the tables (probably twice, if there's a Steam release). I also think that the variable pricing across the tables bodes well for Addams Family or Twilight Zone, as the one that's the most expensive (Ripley, $3.99) is the one that has a specific non-pinball license.