Honestly I think most of your thumbnails are good, they are bright and really draw my attention and are simple (meaning not over cluttered with things )
Its nice to see you have taken some time to fill out the about page of your channel and have included social media links as well in your banner - the only thing I would suggest is potentially looking to relocate your written twitter and FB ID's to the right of your banner just to make them a little easier to read as they do sort of blend into the background where they currently are.
Another thing and this is just my personal opinion is be more active in your replies - I can see that you have replied to some comments on your videos but not all of them, while your still relatively small (in the grand scheme of things and aren't getting inundated with comments) its always a good idea to respond to as many as you can. Also I didn't manage to see your upload schedule anywhere
Finally with regards to your videos it might be worth you uploading videos in bulk if it relates to a series for example having a week or two of Prince of Persia videos ( so viewers know what to expect) though switching it up is also a good idea if you want to show the range of things you do - so really this is your choice. The last thing I will say is when you overly music to your videos I would rewatch them again as some videos the music doesn't really help whats going on and made me question why you picked it.
Anyway thats my opinion - hope it helps