I've been thinking about this for a while, to be honest. I really did enjoy Demigod, and felt it didn't get the launch and sales it deserved. With that in mind, there are few things I think need to be done to ensure Demigod 2 doesn't fall prey to the same troubles that befell the original Demigod, and then there are a few things which the sequel would need to do in order to surpass the original. I'm not a professional developer - take these with a grain of salt.
So, things Demigod 2 needs to do in order to avoid Demigods problems:
First, and most obviously, is simply that the online multiplayer component needs a proper open Beta. This will serve two purposes: getting the whole thing up and running and properly stress tested prior to launch, and offering up a Demo to help people get back on board with the Demigod series. Demigod has a reputation for it's terrible launch, and this will help address that is the best way possible: let the game speak for itself.
Secondly, Demigod suffered from a lack of maps. This was primarily due to the way the maps were constructed. While they enabled the game to have some utterly gorgeous visuals, they simply prevented the game from having that needed custom content to keep it alive once the novelty had worn off. I don't care how it's addressed - but it's something we need from day one.
Lastly, is simply balance and glitches. We understand that games take a long time to get right and aren't perfect at launch - but the developer needs to be able to provide the necessary attention in order to get it there. If the developer isn't able to release a balance patch and bug stomp patch every little while, then it's hard to remain on board for the long haul. Once a game is stable, glitch free and balanced, players will continue to play it for years. DotA, Counter-Strike, Starcraft, Quake 3, etc.
Now, the things Demigod 2 needs to do in order to surpass Demigod:
Firstly, don't for the love God dumb the game down. Supreme Commander 2 is utterly generic and absolutely destroys all that made Supreme Commander the beast that it is. Don't let Gas Powered Games make the same mistake with Demigod 2. Demigod was different to DotA in that it wasn't about Actions per Second - it was about team work, and overall strategy. Becuase it was different, it worked out its own niche. Demigod 2 needs to use it's differences as it's strengths - don't try to out-DotA DotA. The game will fail. Supreme Commander 2 tried to out-Starcraft Starcraft II. I don't need to detail what happened when it was released.
Secondly, social features and eSport features need to be in the box. Replays, replay viewer, proper working lobby system with numerous options, robust friends list (Starcraft II's system is fucking horrendous - use something else as your blueprint) and some kind of viewable, online profile complete with detailed statistics. On top of this, the match making service needs to work well and the ladder system both needs to work, and have an avenue for explination. Perhaps when viewing the ladder you can also view a short embedded video explaining the system in plain and simple terms.
Thirdly, Demigod had a few problems with the basic design that lead to some issues, including but not limited to stacking Demigods, which enabled some serious abuse. Multi-shotting Demigods from across the map isn't fun. Stacking powerful DoTs for an easy victory isn't fun. Having a single dedicated healing Demigod isn't fun. This kind of stuff needs to be addressed in order for it to be easily picked up, and yet still interesting some time later. Team work doesn't mean that I sit back and Heal, or Tank, or DPS. It's a tough line to walk, but it needs to be walked.
Forthly, adding some extra spice that the other MOBAs don't have and embracing the personality. The Dark and Light side thing is interesting, however it's completely ignored. Having different Creeps for each side, and different Demigod skins for each side, is a great step towards making them feel like truly different sides as opposed to simply being different teams. The Towers are a great example of this. Extending this throughout the rest of the game - imagine different effects for each Demigod's abilities based on their side - makes Demigod 2 feel like it's own game, as opposed to DotA Rip Off #19.
Fifthly, is simply variety. Demigod launched with 5v5 maps, however it was way above what the majority of the community was able to play on for technical reasons. 3v3 seemed to be the sweet spot, however that left us with one map that people enjoyed. One. Unless the technical shortcomings can be removed - and that's frankly doubtful - 3v3 needs to be the focus of the developers map making efforts. On top of this, more Demigods themselves are needed. The personality and variety of them is already excellent - we just need a few more of them.
Instead of launching with 8 Demigods and one playable map, Demigod 2 needs to launch with - say - 16 Demigods (I'm happy for the entire original cast to return) and six or more 3v3 maps.
Lastly, and this is based on comments surrounding the game, Demigod 2 needs a more significant single player aspect. According to offical stats, more people played Demigod singleplayer than multiplayer. Instead of a poor Mortal Kombat style tournament ladder, we need a real campaign. We're trying to become immortal Gods - the single player needs to reflect this type of epic setting! A small "You Win" screen at the end is frankly insufficent. Coupled with this is - of course - A.I. The A.I. needs to be able to keep up, and at least pose a challenge without needing to result to cheating in order to not die in a matter of seconds.
Anyway, that's my thoughts. Hope they are useful