The most important question... Why should I upgrade from windows 7 ultimate??? I like it, I'm used to it, And I use windows media player all the time.
Windows media player will still be around. Are you referring to media center? For Windows 8 users, the biggest change is the start menu, and Microsoft edge, the new browser.
Yes, Windows Media Player is in Windows 8 and will be in Windows 10. Even so, I prefer to use Media Player Classic that's packed into the K-Lite Codec Pack. It's free, "lighter" and supports a whole lot more codecs. Most of us never use Windows Media Center :
There's no need for codec pack anymore. You shouldn't be using mpc. Mpc had not been updated since 2008. What you should be using is mpc-hc with all common codecs included. I also use vlc as an alternative. Both don't need codec pack.
You don't need k-lite codec pack to use mpc-hc. New mpc-hc will play most media without additional codec pack.
I use MPC-HC only but my mom is still more comfortable with the media player from the vista generation whereby you can enable the media player playlist to show at all times. Once enable, it just shows. So, I installed the windows media player for her. But once Windows Updates did something, it goes bonkers... have to do it all over again. Sigh... I wonder why Microsoft can't just let us enable the playlist in its latest media player to show at all times.
I started using it because some video files used weird codecs that wouldn't play on Windows Media Player and just got into the habit of installing the Mega Pack. LOL...