They have all kind of games, not only sidescrollers and platformers, You'll find, FPS, Adventure, Puzzles, and others without a clasification taditional. For example the game Narbucular Drop is a precursor of PORTAL
You want fun, a game I wrote is on the site:
I need to get a copy of their JS version of DosBOX, looks way better than the Java version I'm using on my site.
Though as Lazy Game Reviews pointed out, apparently I didn't get the memo that people don't write games for DOS anymore. What makes that game so much fun from a tech point of view is that's actually NOT a graphics mode, it's the 80x25 text mode tweaked to display 160x100 graphics in 16 colours, instead of the horrible 4 colour you would usually associate with CGA. Unlike most implementations of that mode, my codebase works on CGA, Tandy/Jr, EGA, and VGA aspect-correct. The hardest of those to implement was actually the EGA version, as I had to trick it into thinking a CGA display was connected to force the display info for 200 lines instead of 350.
There's a version 2.0 in the works with better sound and joystick support, with a lower system target. My original design target was for a original 1982 PC with a CGA card in the 256k single floppy config. The new target is a 128k PCJr, which thanks to video memory being shared with system RAM is actually ~40% slower than a regular PC. Also expanding sound support for a bunch of devices nobody has ever heard of like the SSI 2001 (aka C64 SID on a PC card) and the mockingboard PC.
It's actually a cute side effect of emulation – if you write a game for the old DOS platform, it's now easier to deploy to windows/linux/OSX/iOS/Android than it is working in a modern language/environment.... as they proved at the Archive, you can simply deploy it off a website if need be.