The Blade series has done it all backwards. It started on a high that proved to big to top, and has conceded ground over the course of the series. Blade Trinity, the third and (hopefully) final part, does not regress this trend.
The original film had a powerful main villain who became a God (played by Stephen Dorff), the second had Luke Goss as the tortured head of the Reapers (a character that had more depth than the original’s Deacon Frost), and Blade Trinity has Dracula (only in it for the name) and a bunch of annoying vampires with vague motivations.
The original film had some decent sword and gunplay. The sequel had seamless live action to CG (with great use of depth of field) long before The Matrix Reloaded touted it for the ‘burlyman’ sequence. The third film has some lo-fi fights, nothing impressive. For what is essentially an action film, it got it all wrong.
More than anything this film suffered due to its lineage. That is not to say it is a bad film (the humour was hit or miss but still an appreciated addition), it was just lacklustre compared to what has gone before.