Folks definitely seem to like The Harvest; I personally didn't find it very enjoyable at all. I will 100% second ilomilo, though. One of my favorite games ever. It's a lot better on the Xbox, but still great on the phone. And of course, Plants Vs. Zombies provides hours of mindless fun. I've played the hell out of that game on PC, Xbox 360, and DS and I plan on eventually doing it again on my phone.
Anyway...I too recently jumped on the bandwagon. I've had my Windows Phone for about a month now, I think, and I'm very pleased with it. The selection of games is lacking somewhat, but there are still some gems available. I know it sounds daunting, but I actually just went through the list on the first page in this thread and downloaded the demo of every single game (and wrote down which ones I liked and how much they cost). Found lots of goodies that way.
Oh, and be sure to check out the FREE Xbox Live games like Minesweeper, Wordament, and a few others. As far as free non-Live games go, I haven't played a whole lot, but I would recommend Call of Carlos, Incredible Circus, Monster Stack (1 and 2), and Zombeee.
EDIT: Ha! I just realized I made a PvZ pun!