Just Watched Underworld: Blood Wars - Selene's Still Got It?

Okay, so I'm on this whole classic movie dive, right? And a buddy was like, 'Dude, you HAVE to see Underworld.' So I started with Blood Wars (2016)... I know, I know, jumping in mid-series, but honestly, the visuals were crazy. Kate Beckinsale is still owning it as Selene. I'm a sucker for that dark, gothic style, and the action scenes were intense. I'm kind of hooked now, but I'm also a little lost. Like, what's the deal with Marius and his super-Lycan army? They seemed way more powerful than the Lycans in, like, any other vampire movie I've ever seen. And I'm trying to follow who betrayed who amongst the vampires, but it's kind of a mess. David seems cool, though. He and Selene have a good dynamic. My question is: Does this film connect well to the earlier ones, or did they just, like, change everything? I'm wondering if it's better to go back and watch the others now, or if they feel totally different from each other. Should I be expecting this type of Lycan strength in the other films? Were the original films more character-driven or action-based like this one? Also, side note: the Nordic vampires were a bit odd. Were they a last-minute addition or are they a big part of the Underworld lore? Curious to hear what the long-time fans think since I'm totally new to all this!