I have a 2007 MacBook3,1 myself. I’m afraid you’re probably expecting too much from a machine that Apple decided was obsolete way back in 2012 when macOS 10.8 Mountain Lion came out. It was stuck on 10.7 Lion and getting pretty useless as far as current web browser support. It’s kind of a miracle that it still works as well as it does. It only has the basic Intel integrated graphics so it’s unlikely we can get more performance by looking for different drivers. Try watching YouTube at a lower bitrate instead, like 480p or even 360p. It doesn’t really make that much noticeable difference with most video content but it will drastically decrease the work the GPU has to do.
That being said, are you aware that you can upgrade the MacBook3,1 all the way to 10.11 El Capitan? It actually works surprisingly well. But I don’t think it works any better with heavy video content than eOS does. Probably even worse actually, because full graphics acceleration isn’t working yet in the patched El Cap. The installer patcher is at https://github.com/rmc-team/osx-patcher in case you want to check it out. It’s at least a lot more useful with El Cap than with Lion, and its fun to dual boot El Cap with eOS to compare them on the same hardware.
Also if you are missing the Mac-style keyboard shortcuts in eOS try to look up a new project called Kinto. You’ll find it by googling rbreaves-kinto. It’s not perfect but it’s progressing well.
With my still limited knowledge of Linux here is what I would try to fix your problem. Let the desktop start up, then try to access another tty “console” using the function keys. How you do this seems to vary a bit between distros, but usually it’s either Ctrl+Alt+F1 (or F2, F4, F4, up to F7) or just Alt+F1. Since you’re on a MacBook, you will probably need to use the “Fn” function key to actually activate the function keys.
If this works you get a black screen with a text login prompt, where you can log in and try to troubleshoot.
If you can’t get to another console because the keyboard is truly unresponsive, you’ll have to boot from some kind of live Linux media like the USB stick you may have used to install eOS in the first place. Of course then you’d have to figure out how to mount your encrypted drive partition. It shouldn’t be too difficult but I’ve never done it.
If you did get to another text console you can do a couple of different things. One is you can try to uninstall the package that installed the Intel driver you thought you needed. If you can’t recall the exact package name you can try “sudo apt search packagename” (use some relevant word like “intel” instead of “packagename” obviously) and then when you find it you can try “sudo apt remove packagename”. Then if it’s successfully removed, do “sudo reboot”. See if the desktop comes back after the reboot and the keyboard and mouse work again.
If that didn’t get the keyboard back, the next thing I would try is removing the configuration file that tells the graphical interface what driver to use. Using the same procedure from above to get to a text console, type this:
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.broken
This just renames the xorg.conf file to xorg.conf.broken.
If for some reason you ever want to put it back, just reverse the file names or make a copy like this:
sudo cp /etc/X11/xorg.conf.broken /etc/X11/xorg.conf
But don’t do that right now.
The current Xorg server can supposedly auto-configure itself in the event that there is no xorg.conf file found. To see if removing the xorg.conf file will let it fix itself, do “sudo reboot” again.
If that still didn’t work, you will need more expert help than I can provide, or you may need to try reinstalling eOS. That should be possible without destroying your data, as long as you can manage to mount your encrypted drive. But again, I’ve never really done that.
Another possible solution, after uninstalling the extra Intel package and removing xorg.conf, is running “X -configure”. I’ve tried that on other machines and Linux distros without much luck, but maybe it will build a new working xorg.conf for you.