I've been reading Marvel Comics for a while now, so when a concept comes along that makes me look up from the habitual reading of all things superheroic and say, "Wow, that's kind of cool.", it must be something truly interesting. The Sentry is one of those concepts. Unfortunately for the poor reader, while being truly interesting, The Sentry is one of the most misused, confusing, and all-around banged up characters currently being utilized in modern day comics.
Originally, the Sentry was a scam created by Marvel to answer the question: "What if there was a hero that not only the Marvel Universe forgot about, but the reader as well." It was some tricknology that attempted to break the 4th wall between the reader and the comic and for the most part it worked.
There were articles in
Wizard Magazine and other trade rags that were "leaked" for the set-up and then a 10-issue series (5 numbered and 5 one-shots) by Jae Lee, Paul Jenkins and the master of the Marvel gimmick Stan "The Man" Lee which told the story of sad sack
Robert Reynolds, The Sentry (a hero with the power of a million exploding suns - more on this in a bit) and the case of ultra amnesia he inflicted on everyone to defeat his greatest enemy, The
Void.
**Spoiler Alert**Now the twist for your melon is, the Sentry and the Void are 2 halves of the same being, because he's a schizo. Therefore, the only way he can defeat himself is to make everyone, including himself, the entire Marvel Universe, and the reader forget he ever existed. This should give you an idea of the power level we are dealing with. If you can make Galactus (one of the first beings born into the universe) forget who you are because you want to, well you're pretty badass.**End Spoiler Alert**
All of this was well and good. The limited series had some success as a cerebral, self-contained, and slightly wacky but well-done experiment and it was left well enough alone. That is, until the filthy, chubby hands of one
Brian Michael Bendis decided to bring the Sentry back for use in
New Avengers #1. Now don't get me wrong, I like BMB's work in most cases. However, I've found him to occasionally be a writer who takes a concept to a certain point and then leaves it broken and sitting in the corner like a doll missing one of its eyes and both legs for someone else to fix to play with. Sentry was retconned back into the Marvel U, had some stories told about him for 4 or 5 issues and then set loose to play in the mainline Marvel Universe continuity. Another limited series followed (which retconned his origin again), followed by various appearances in the
New Avengers,
Mighty Avengers, and most recently,
The Dark Avengers (See a theme here?).

Now here's my bitch, Sentry has been described as having the power of a "Million Exploding Suns" and having been transformed by a chemical concoction "100,000 times as powerful as the super solider serum which made Captain America". His signature move is to throw shit which annoys him into the fucking sun. How do you handle a character like that? Original plans were discussed which made him like a great white shark - For example, if Shocker and his D-bag squad are fighting Squirrel Girl and the Great Lakes Avengers (no shit - not making them up, click the links, really) and Sentry flies over, everyone quits what they are doing and acts like they are minding their own business.
However, rather than go this route, it was decided that Sentry would have a basically crippling form of totally unpredictable mental illness, which causes his powers to fluctuate wildly. One minute he's lifting aircraft carriers and choke-slamming Sub-Mariner's pet man-whale Giganto, the next he's afraid to go outside his ranch-style home. Balls. He gets bitched by Ultron in a titty-tastic Frank Cho issue of Mighty Avengers and then, a few months later goes toe to toe with a Hulk so enraged he can "break the world". Double Balls.
In conclusion, I'm still really rooting for the Sentry. I think the character is awesome as a flawed giant in the Marvel Universe and if they can lock him down with a stable set of powers and ideas, I think he'll continue to be awesome. It's rumored that Bendis is getting back to the Sentry in Dark Avengers #3 and hopefully this will straighten him out (and maybe answer what the hell he saw in the rings of Saturn that made him cry boo-hoo again). However, given Marvel's past track record for dealing with complex character problems of late (One More Day anyone?) I'm not going to bet that the Sentry will be any more unfucked before the end of the year.