Elecbyte is currently releasing RC (Release Candidates) of this series. They are not new versions, but rather beta versions released to the general gaming public. It hasn't been until recently (as in September 2009) that Elecbyte has gone back to try to renovate MUGEN with some newer versions. Newer versions now support high-definition resolutions.
UPDATE (2/12/2010): I have unveiled a MUGEN project I was working on in this blog entry. It concerns a number of characters I've conceptualized.
The fighting dynamics themselves are simple. You have your basic big health gauge followed by a Super gauge for more powerful moves and combos. Many fighters have their own fighting systems, like Street Fighter Alpha 3 characters for instance. So this game can consist of a convergence of different fighters with different fighting systems.
If you just have MUGEN at its most basic from the most recent full version, you get only one character and two stages. The iconic fighter of MUGEN is Kung Fu Man, also known simply as KFM. His moves are fairly basic. There was even supposed to be a boss character called Suave Dude, whom KFM is looking to beat down to save his girlfriend. However, he was never finished (I believe). But if you REALLY want to enjoy going with a wide variety of characters and stages, you'll need go get many more characters. The site I recommend you get characters from is MUGENation, which features lots of characters and stages and is usually the first source to look to for new characters and stages.
You can download screenpacks to turn the dull default arrangement of graphics to more interesting ones. The most popular is EVE (Everything vs. Everything) Battle. I have BROKEN and use Kamek's Super Mario Bros. Melee-inspired screenpack. Screenpacks come complete with graphics, sounds, life bars, in-game fonts, and more.
* E - The weakest fighters. They either get beaten very easily or don't have as much firepower to contend with stronger fighters. Good Angel is an example of an E-Class fighter under my scheme.
* D - Stronger than E-Class fighters, but not good enough to be among elites.
* C - Middle of the road. Not good, but not great either.
* B - Very talented fighters with great fighting skill. However, they aren't good enough to compete among the elites.
* A - The elite class featuring the strongest fighters and the most intense competition. Chiho Masuda of the Variable Geo series is an example of an A-Class fighter.
* Superlative - Fighters whose capabilities are so strong, that they are almost unfair to fight against. A Superlative ranking is NOT an honor. It just means that the fighter is immensely strong and very difficult to beat. Characters like Ella, Ultimate Rugal, and God Orochi are examples of Superlative-class fighters.
* Experimental/Independent - Fighters that don't belong in any sort of performance index, or fighters that aren't among anyone I use often. Two characters I've deemed part of this class include Rose of the Street Fighter Alpha series and Dark Arcueid because their level of competitiveness is difficult to actually gauge.
I enable the Debug keys in my MUGEN runs. I have three-round matches that last for infinite time. If there's some kind of situation where a glitch happens in the match or something (like a character that jumps too high in the air and doesn't ocme back down for over five or ten seconds), I immediately call for Time. If a three-round match goes to the Final Round or a match series (like Best-of-Seven) goes into the Final Round, I set the Final Round to be All-Out. All-Out meaning all fighters will be at full health and full Super strength for the Final Round. This makes for that exciting Final Round to determine who wins it all. I even set all fighters at full strength (a term I use to mean "full Super strength") if a fighter wins by a Super Combo Finish. The negative to this is that some fighters are immensely powerful at full Super strength, so I have some exceptions as to who gets set to full Super Strength.
Now on to how I determine rankings. The rankings I discussed are not permanent. I have a system in which fighters can be promoted or demoted to different classes. If a fighter of a lower class beats an opponent of a higher class, then the lower-ranked fighter will have the chance to be promoted to a higher class. The way that is accomplished is that he or she must fight against a team of four fighters of the higher ranking class. If he/she beats all four, then that fighter is promoted to the next level. If a fighter of a higher class stumbles to beat fighters of a lower class, he/she may be demoted. To avoid being demoted, the fighter must beat four opponents within his/her own class to avoid demotion. The fighter will be demoted to a lower class.
Among each class of fighter (excluding the Superlative and Experimental/Independent classes) are Class Champions. They are determined by the fighter within each class that is the best of all fighters in their respective class. A #1 contender is determined by whomever is the strongest fighter who is good enough to contend for the title of Class Champion for each of the five eligible classes. Each class champion is eligible for one chance at promotion.
There are also sub-classes based on game series. For example, I have characters in my MUGEN roster from the Asuka 120% series and Variable Geo series that comprise their own classes. My Variable Geo roster has three classes- VG2, VG1, and VG-Super. Characters within each sub-class have both an overall class rating as well as ratings within their respective sub-classes. Within sub-classes, there is a ranking system. The rankings for each fighter can be increased or declined with victory against higher seeds. A sub-class championship is determined by whomever #1 and #2 are. Championships can also be decided by tournaments. I set up a three-round series where multiple fighters have the chance to compete for class champion. There's even a 3rd Place fight to determine third place in the tournament.
I'm actually trying to create my own fighters, but all from scratch (or mostly from scratch). I haven't made any real progress because that's a lot of work for me to try to create characters from graphics to moves to things like that. At the most, all I've done was come up with palettes I think they'll use. I announced on Twitter that I'd come up with a new category called "Fictional Characters." The reason why I haven't come up with it is because I haven't made any characters (or at least drawings of them) to use in describing my characters. Most of the ones I want to create come from a concept I've had lined up for MUGEN dating back to the Summer of 2008.
Overall, I enjoy MUGEN for all it's worth. It's a great deal. Greater deal since Elecbyte has come back on to dust off MUGEN and give it some new blood. I can be sure that MUGEN will only be better when the latest full MUGEN is unveiled. So give MUGEN a try!
UPDATE: 5/5/2010 - If you want to learn more about Suave Dude, "Suaves" was just released on Elecbyte's blog.