I was actually recently trying to figure out how I would implement a Trapper class for a 4e-derived heartbreaker as a controller for a Device power source (an Alchemist would also be a Device user), but I was having trouble getting it to work right. More than any other class they would be terrain dependent. In an open area, they might be pretty useless without some significant forced-movement abilities since an enemy could avoid whatever snares, caltrops, marbles, or whatever you set. In tight spaces, they might be crazy powerful since enemies would be forced to move through the zones created by their abilities as there is no other place to go. The alternative of creating semi-autonomous stationary-pet turrets would be a lot easier to get working, but thematically doesn't quite fit (although it might work for a sub-class or paragon path or something).

Getting the "deals with many enemies" and the "cripples the enemy" roles to mesh is a little tricky to do with a martial character. A BFS wielder who uses lots of large swings and cleaving attacks (hitting multiple enemies, adjacent enemies, or a blast) could do the former, whereas a brawler/pugilist character who grapples, trips, pins, and otherwise fights dirty to inflict slow, immobilize, stun, etc could do the latter. I could see knockback, tripping, or DoTs from getting hit by a giant sword that cleaves through multiple targets, but it probably wouldn't do some of the weirder things that controllers can do; this character would be a striker first and a controller second.

A grenadier could be a controller, by throwing different types of bombs with special effects, but it would be debatable whether they would even be a martial character.