Pain's a good set, and is rather soloable, though once you get to high levels you may find that teams can generally do well enough without you, even moreso at 50 when people stop running at +levels. You may find yourself only bringing the character out for really hard things like the LRSF or the Incarnate trials (if the sneak peek on test is any indication). That's where I am with my Empath.
Personally, I think the set is worse off for having World of Pain instead of Fortitude, and having a large self-buff on the rez sort of sends the wrong message.
Issue 16 made me feel like this.
Warning: This poster likes to play Devil's Advocate.
I have a lvl 4X Dark/Pain corruptor. I knew that Dark Blast wasn't the best choice for a primary but I wanted it for concept reasons 
(seriously I feel like playing a weak defender... wait, no, my defenders feel stronger).
Compared to Empathy and Thermal (which have a lot of similarities), Pain is way less busier because you neither have to keep an eye on Fortitude or Forge, nor to refresh 2 resist shields on all your teammates every 4 minutes. Everything comes in a handy PBAoE buff. At low level you can't make it perma like you could with Thermal shields, but it gives you plenty of time to use your primary. The damage buffs attached to Share pain and Conduit of pain should motivate you even more. It's the main reason why I would not recommend Dark as a primary for Pain: even with those damage buffs, I only see a cloud of ridiculously low numbers (ok, figures) when I use my blasts 
For the moment I prefer my Empath troller (for its AoE Recovery buff and Fortitude which are always useful) and my Thermal corruptor (for his versatility) over my Pain corruptor, but maybe it would not be the case if I had chosen a more damaging primary.
I have a DP/Pain that I like but it more for the sets synergy that /pain alone. I went with pain b/c I wanted to try a heal set and don't really like casting shields in thermal and wanted a -res power that empathy is lacking. World of Pain's buff also applies to the caster so that is a + for pain as well.
The -damage ammo in DP helps with /pain and in the teams that do not need the extra protection I can always switch to fire rounds for more damage. My favorite trick is that Hail of bullets (the mini nuke of the set) and Anguishing cry (the -def and -res) are both PBAOE and both on the same timer. It is a nice one-two one teams. Soothing aura also runs during the long animation of HoB to help survivablility a bit.
My fire/pain corruptor is awesome. She can switch between being a damage monster or a healbot in a heartbeat. Whichever the team needs at the moment. Add to that a decent aoe debuff, a very good aoe buff and the awesome that is Painbringer.
Imo paindom > thermal (the set it resembles most) for the sole reason that you don't have 2 single target shields to apply every 2 seconds (slight hyperbole). Instead it's just the 1 aoe.
@True Metal
Co-leader of Callous Crew SG. Based on Union server.
I'm debating on what corruptor to roll right now. I wouldn't mind being a support toon but is pain domination really the best choice? Im not sure if the heals are worth it when you can go rad,kin,coldmsonic,TA etc... The only real /Pain I have seen would be a Sonic/Pain.
Just looking for some insight baout the set.
@Nova King