A 3/2 hits really hard and trades off with a lot of creatures in combat, and a few early surveils help to set up your early turns
However, if a player isn't already in a dungeon when they venture into Undercity, that player doesn't get to choose which dungeon card to put into the command zone
This combination of exiling removal, combat trickery, and card-draw creates an extremely flexible card to run
Whether you look for a flare as a free spell, a fetch land, or a feline (namely Ocelot Pride), you could land on a great boost for your Modern deck
If you just need to curve out and you have some ability to pump the card later it fills this role admirably
The trick with Grevens ability is to use creatures that have higher power (cards you draw) than toughness (life you lose)