I just joined this forum today, and am noticing a trend after reading topics for a few hours. There is a link in the broker rating forum with over 100 negative reviews of forex.com. I stopped reading after 100 of them.
Forex.com is the only platform I have known. Just over a year ago I started paper trading with them until I was comfortable enough to risk my hard earned money. (up 60% in a month) It took me about a month to lose $500 in my mini account. I went back to paper trading, and started trading real cash again just one month ago. I have been trading very nearly every day since opening that practice account just over a year ago. I am currently up 90% with the $300 I deposited a month ago. Here is my opinion of Gain Capital's forex.com
Service: Excellent, I have had email responses in less than an hour on several occasions. Very friendly, courteous, and professional over the phone. I never traded over the phone, but have had lots of communication with them, every time has been a positive experience.
Platform: Their windows platform is glitchy and kind of the pits. There are a lot of things great about it, but it is obviously still a beta platform. Examples are placing an order and corresponding stop loss + limit, or trailing stop in 4 clicks of the mouse. Orders and position are then indicated on the charts. I say it's obviously beta, because it sometimes crashes, and the charts don't like it if you switch around between time periods or pairs too quickly. I actually generally prefer the java platform, although there are a few nice features the windows platform has that the java does not. For example I love being able to see my position and orders indicated on the chart, which is not done on the java platform.
Spreads: Have been pretty aweful the last few months with all the economic craziness. I've seen USD/CAD over 12pip during volatile movements, although that sort of spread only lasts a second or two. Usually see 5.5 or 6 pip for that pair, generally closer to 3 pip for EUR/USD. I definitely never noticed a spread anywhere near the 8-10 pip range when trading a year ago.
Rollover: I don't know how their rates compare, but going down the list, there was a pair or two that would cost you no matter which direction your position is in, so something is not right there. Currently their best rollover rate is if you are short GBP/NZD. The rollover is worth 3 pip or so in that situation.
I hope my little review helps. I don't have any complaints with forex.com, but am also aware that I have nothing to compare it to. I'm at these forums mainly to see what else is worth trying before I dedicate myself to one place. With my miniature account balance, and approach to trading, forex.com has been a wonderful learning experience and I recommend it to anyone.