They felt like an unfinished product, don't remember why.
Is Sanctum fun to play with friends? I'm thorn between buying a single key (3 euros) or four keys (7 euros) on steam.
Sanctum wasn't much fun after a few levels. We ended up playing Dungeon Defenders instead. Still do now and then, great fun with the whole family. Just don't buy Dungeon Defenders 2, it's not as good and very buggy.
One of my favorite tower defenses is Sanctum, on the PC. It's a tower defense with casual FPS elements. (Its sequel I didn't like as much, it's more the other way around as an FPS with casual tower defense elements.)