I would definitely recommend them. Blood Omen is dated technically (plagued with loading times and slowdown, a low budget game) but it's still a great game with a fantastic story, atmosphere and voice acting, and it's available on PSN digitally, as is Soul Reaver, but if you're not just looking to play but to collect I don't know how easy to find the discs are. Soul Reaver 2 is a direct sequel to Soul Reaver (and Defiance a direct sequel to SR2), so while I the original LoK is still my personal favourite, I'd say it's even more important to play Soul Reaver before SR 2 (SR is set many years after the original and sort of starts a new storyline, so playing SR before BO wouldn't be as confusing).
Avoid Blood Omen 2, though. But that will be easy, because that game totally does not exist.
Oh? I didn't know I owned another rarity... >_>