Damn, i really want to give you guys some useful feedback but I don't think I can add anything that Valerik hasn't already mentioned. The tumbnails are probably what stands out the most, the banner part isn't very readable, and it seems there's really not much going on outside of them, so the majority of the thumbnail's space is taken up by... well, not much in particular other than some vaguely recognizable imagery from the game, while any informative text sits cramped at the bottom. As to how you can improve them, I don't rightly know, so I guess this is just useless criticism
But I think just by reorganizing some things around and maybe being more selective with the in-game image you'll be in business, some experimentation may be required.
And then there's the videos themselves. Highly entertaining, but maybe a tad... bloated? Like it seems to me that a little editing would go a long way, I've noticed your videos are mostly a single chunk of commentated gameplay. I think if you just made an effort to trim out some of the fat and leave in the most interesting parts or comments it would really help the videos' dynamics, as well as your length issue. I know some Youtubers who do live comms get like a couple of hours of footage that they talk over and then sift through it leaving only the best bits, resulting in say a 15 min video. Now I know it may be hard to judge what gets tossed and what makes the cut, but I think making an effort to do so, and experimenting a bit can ultimately go a long way and really pay off.
That being said, I like what you guys are doing, I think the fundamental concept, as well as your consistent aesthetic regarding the banner and intros and stuff are really solid and there are ultimately good times to be had with your stuff. I just think a little work on the presentation would help bring those good times to your viewers in a more digestible, and ultimately enjoyable fashion, and that putting some thought into it will more than make up for itself in views and general video quality.
I don't know if I made many sense, I hope I did and that you find something useful in my opinion. Bottom line, keep doing what you're doing, I'd love to see you guys make some noise in the gaming scene. Best of luck in growing your channel!