Both OpenBSD and NetBSD come with XFCE, OpenBox, Firefox, mplayer (or equivalent). NetBSD pkgsrc may be a bit closer to Gentoo than OpenBSD ports/packages, but both are excellent package systems. You may get more games with NetBSD, including Minecraft and others but I haven't checked, so don't quote me on this.
If you are used to Gentoo, picking one or the other should not be too difficult, but OpenBSD, while a bit picky when it comes to hardware, is also a bit easier to use: if a piece of harware is supported, it is supported. Period. NetBSD often requires compiling a specific kernel to add this or that peripheral. OpenBSD usually supports everything out of the box, as long as it is in its harware compatibility list. Plus, there is this schweet schweet security goodness, now with LibreSSL gooey core!
Here is a quick example: I have had a motherboard die on me. I just ripped off the main HDD out, put it into a slightly different machine, and OpenBSD just picked up the harware changes, reconfigured, checked the filesystems and worked without making a fuss. I have used OpenBSD for many years in a second-hand laptop, where everything was supported, and it was a pleasure to use as my main machine. The update procedure is quick and easy, and a new version of the OS comes out every 6 months like clockwork.
So there you go, hope this helps.