I think a 2-3 year development time is very reasonable and see no problem with them making sure it's polished. At least it's not as drawn out as Blizzard's 10+ years development times. Also remember that Runic took some of that time to port Torchlight to other platforms, so it wasn't all devoted to TL2.

Anyway, Torchlight 2 was already fun in the beta weekend I played - so I'm pretty sure they'll release something good.