Rise of the Lycans, the most sophisticated of the Underworld films so far, is still a good time on repeat viewings. The action does peak during the first half but the romantic (and occasionally harlequin) story keeps it chugging at a good clip. Character development may be thrown to the wayside a bit but for people familiar with the predecessors this shouldn't be an issue. Similar to those predecessors, the effects flip between practical effects and CGI though not as elegantly.
For what can be assumed to be sales purposes the film is marketed with the idea that Rhona Mitra is the focus. Not only would the marketing have been more original if the truth of Michael Sheen as the main character was at the forefront but Sheen's Lucian also makes for a fantastic hero. Sheen can carry many different types of characters - I was bummed to see him underused in Frost/Nixon but I greatly look forward to his (hopefully Oscar-buzzing) reprise of his Tony Blair role from The Queen in the upcoming film about the British Prime Minister.
Overall Rise of the Lycans, while including a few stumbles (particularly in the handling of that two-on-many sword fight in the citadel) benefits from having nearly everyone involved in the first two return to contribute and fits perfectly in the mythos while successfully paying tribute to its pre-established fans. I'd rank it as my second favorite Underworld so far. I still like Evolution much more but it's easily better than the original which, for me, struggled to find its footing and even inspired a strong disliking from me before I saw the sequel.
I might also mention that Bill Nighy's third outing as Viktor in Rise quite probably firms him up as the best on-screen vampire since Gary Oldman in Coppola's Dracula, in my opinion (in a classic sense, thereby excluding the excellent likes of Dorff's Frost and Goss' Nomak in Blade and Blade II, respectively).