I downloaded the game, and from a few plays it is more or less the same as PVZ1. I haven't gone to the time travelling features yet but one neat (free) addition is the ability to temporarily supercharge your plants using seeds. The graphics are simpler but that's because each animated character now has more animation. Each character seems to have more 'bounce' and movement and fluid animation does make the game play better.
Unfortunately it looks like EA has really restricted the use of our favourite plants from PVZ1 to purchase-only upgrades. Favourites now cost $1.99 each (edit: $2.99? seriously! I bet this will drop to $1.99)
I think this is only going to make PVZ1 more popular.
Screenshots of Plants VS Zombies being EA'd
http://www.flickr.com/photos/83548270@N00/sets/72157634573159324/
And the screenshot that will make PVZ fans cry:
Image
That sure makes me cry, i loved all those plants (besides snow pea which is just f***in' stupid.