I'm in love with Jesus and proud of it!
Grenade spamming is ridiculous in this game. I never got the chance to play a lot of Halo 3, but I'm sure it wasn't as much of an issue then.
I play Squad Slayer and it's just people lobbing 4-5 grenades at a time... most of which somehow end up under my feet, even if they weren't meant for me. Anyway, it's stupid, because I don't even see anybody using their guns. I've literally stood by and watched as 6 or more frags were flying across the map, most of them exploding nowhere near their intended target.
And then there's the magical poop grenade, where somehow everyone that gets killed mysteriously craps out a mini-nuke. It wouldn't be an issue, except that you're so damn slow in this game that if it's anywhere near your feet you're screwed.
I've even been killed by grenades that were thrown into rooms randomly just because a grenade could be thrown there. It's retarded.
I like the TU, and I like Squad Slayer. But after 5 or 6 games I get so damn sick of mini-nukes flying all over the place I just can't take another match. That's why I play a lot of SWAT and Rumble Pit, because grenade spamming isn't as much of an issue (or in the case of SWAT, nonexistent). TU should limit everybody to only 1 grenade in Squad Slayer IMO. That's half as many grenades being thrown everywhere and twice as many players having to rely more on their trigger fingers.
tl;dr - Grenade spam takes a lot of enjoyment out of the game, especially Squad Slayer.