IMO, it's like reading a sequel to a trilogy. You skip 9/10's of the stuff that happens to set up the next book.
However, like any good author writing a stand alone novel, it's written so that first time readers, or those unfamiliar with that era, can pick it up and know what's going on, as if there wasn't a preceding book/prequel to it (yes I know the KOTOR/TOR is a series/era, but speaking novels of that era, these have been stand alone). If you've ever picked up books that have a protagonist with a history, they don't always go into the extensive details like a prequel will. The SW prequels are awesome, but the original trilogy did well without them, right?
Regardless, you'll miss some important story points if you skip the game's story. You could play the game first, but if you aren't interested in taking that time/money, or aren't interested in those kind of games, or any computer game in-general, then look up the wookieepedia articles. They're pretty accurate as far as I'm concerned, and a quick read. Third option is to go on youtube and watch a walk-through (can skip through none-story parts) or a collections of custscenes from the games. The TOR MMO timeline clip about Revan's era is a fast synopsis, and is although a good watch, IMO doesn't give you a good enough look into the story.
Hope that helps!