I don't personally consider Resident Evil Mercenaries as counting, otherwise I would probably give it to 6.
Dawn of War 2 probably had my favorite horde mode with the Last Stand, though it definitely needed a larger selection of maps. The sort of character customization and variety you had in that game was unrivaled in the sub-genre, IMO. You could be a minion master Tyranid Hive Tyrant, a tricky group-teleporting Eldar, a Chaos Sorcerer stealing the enemy's own units, and so on, and all of these classes could be built in dramatically different ways. Like take that Hive Tyrant and turn it into an enemy shredding, debuffing tank instead.
(A lot of players might suggest DOW2 doesn't count, but I'd argue it gets just as intense as any shooter.)
Mass Effect 3 was great with the different classes but way too RNG-heavy for progress.
Most recently I was really impressed with the Frontier Defense added to Titanfall 2. There's good diversity, the matches don't last very good, Titanfall 2 already has really good combat -- it's a lot of fun.