My anwser will be a bit bias as you will probably tell from the Y/A avatar picture as well as the last name of my username. With that.
Yes Hellsing Ultimate is a good anime. It is heavily focused on the dark "fantasy" genre, and really focuses on content that many people will find highly graphic and offensive. Mainly the typical violance, blood, and ect... The anime does pretty much closely follow the manga. However there are some area's to pick at. Some song choices seem to be "missed placed" and "not correct" for that specific scene. With that some of the best songs actually being used in the credits. There are alos some scenes that just seem weird for the series. This is mostly seen as a form of comedic relief an attempt to take a short break from the dark, gritty, and blood bath. Personally I don't like it, but ultimately these scenes were put in place due to the lead director taking some creative liberties. You can really see it in the Anime series: "Drifters".
Has a pretty soild anime story, however there are two instances near the ending that leaves players confused: Some slight spoilers. Near the end with the "Betrayal" scene. It's not really shown as to why this character is betraying all of the others. This is because the series never really focused on it, this is probably due to time constraints. There was a "mini-series" or a 1 episode sereies I think that is called "Hellsing: The Dawn" shows the back story of the main characters and antagonist as well as why the betrayal happens.
As for the final climatic ending. You'll want to research the Therory/Thought Experiment of Schrödingers Cat. But even that itself is confusing.
There are only 10 episodes. However episodes 1 - 9 are 1 hour long, and I think episode 10 is an 1 hour and 30 minutes long.