Beam Rifle has some really good synergies. I've been playing with it and having a good time.
Its got a solid mechanic in Disintegrate, since you can auto put it on with a high damage attack followed by an instant snipe and the quick basic shot.
IT has a solid -resit debuff, as well as good damage types.
It has fast attacks.
If you like guns instead of casting, beam rifles come in a wide variety, from rifles to goofy gadgets.
I've been using it with Time and its nice, because it has a stun that stacks with Time Stop, and a hard swing attack chain that you can weave into support to blow up harder targets. There are always bosses to target, and its pretty easy to Disintegrate / Shot to spread the love DOT around.
I admit it has terrible AOE, like just terrible, so I don't think its great for burning down packs but between the stun from Time and Beam Rifle, it does decent Solo since it easily locks down targets and does decent AOE as long as the dps isn't so high everything instantly dies.
Between Time and Beam it puts out -650% Regen for AV targets, always nice to have on a defender, as well as throwing out Mag 8 Stuns.
I'd recommend it with any spec that has a stun or a good AOE slow, its a good powerset with some nice perks for groups.