was never close to finishing the main quest, but i have a question: does completing it end the game, like u cant do other stuff?

No, the game continues afterward.

thx - not that i think i will EVER complete it... for whatever reason, i still see everything in VEEERY sloooowwww motion... battles mainly.

What platform are you playing it on? If it's a PC, it sounds like your computer might not be good enough to run it properly.

No the game continues.