Marvel Star Wars was the first Expanded Universe comic series, launching just after the premiere of Episode IV: A New Hope with an adaptation of the film. The series ran from 1977 to 1986, lasting for 107 regular issues, three annual issues and a separate four-issue adaptation of Episode VI: Return of the Jedi. Most of the storyline takes place in between the three movies, following the continuing adventures of the Rebel Alliance.
Tone of Marvel Star Wars
It feels awkward to accuse some of the earliest Expanded Universe works of not "feeling" like Star Wars -- that nebulous, indefinable quality to which all Expanded Universe works must aspire. But the fact of the matter is that there's just something off about the way Marvel Star Wars feels in the Star Wars universe.
The general tone of the storylines and the type of adventures our heroes encounter have much more in common with the early sci-fi serials Lucas was imitating in the first place than the Expanded Universe we have today. That's not necessarily a bad thing, but it does take some getting used to, and contributes -- even more so than the continuity errors and silly characters -- to the sense of separation between Marvel Star Wars and the rest of the EU.
Characters in Marvel Star Wars
Marvel Star Wars is perhaps best known for its silly characters. The most famously hated is Jaxxon, a 6-foot-tall carnivorous green rabbit smuggler. Any two of those things would feel silly, but Marvel Star Wars had to go and put them all together. To be fair, Jaxxon doesn't really deserve as much flack as he gets. He only appears in five issues at the very beginning of the series, before the story really gets its footing.
The series actually gave us some very interesting characters, particularly in the villain department. The Tagge family are the main antagonists for much of the series -- to avoid too many anticlimactic confrontations with Darth Vader -- including Baron Orman Tagge, a blind human who trained himself to use a lightsaber, despite not having any Force abilities, in the hopes of taking revenge on Darth Vader. The later issues of Marvel Star Wars introduce Lumiya, a part-cyborg Sith Lady and Vader's apprentice.
Continuity of Marvel Star Wars
Like many early Expanded Universe works, such as Splinter of the Mind's Eye, Marvel Star Wars is also well-known for its contradictions with later established continuity. For example, the first annual issue establishes Anakin Skywalker and Darth Vader as two separate people, and early appearances of Jabba the Hutt, before he was established to be a huge, slug-like alien in Return of the Jedi, portray him as a yellow-skinned humanoid with prominent whiskers.
Lucasfilm was much less concerned with continuity back then than they are now (there's even a person whose sole job is to keep track of Star Wars canon). To correct that fact, they've relegated Marvel Star Wars to that special area of canon that basically amounts to "not canon except for the parts that are" -- which is to say, the events of Marvel Star Wars didn't really happen in the Star Wars universe unless they're referenced by other, more authoritative works.
This happens, however, a lot more than most Star Wars fans unfamiliar with the series will probably notice, both in small ways (like using Orman Tagge's image for the logo of fast food chain Biscuit Baron) and large ways (like Lumiya reappearing in Legacy of the Force). In fact, according to Wookieepedia, so much of Marvel Star Wars has been referenced in other works that we can practically consider the whole thing canon.
Marvel Star Wars Collections
The issues of Marvel Star Wars have appeared in several paperback collections of early Star Wars comics, including Classic Star Wars and the A Long Time Ago... omnibus series, the first volume of which was published in June 2010. It's great that Lucasfilm is making these previously hard-to-find comics more available to fans, because they're really quite interesting. Despite the often cheesy story and characters, Marvel Star Wars comics are a fun read in their own right, not just because they're part of Star Wars history.