There is no "one" thing. As said before there are numerous small things that kill the fun in the game. Here are some of my top examples (all of these have been posted about numerous times):
1) The UI sucks, specifically:
-- too many mousclicks overall
-- too many double-clicks
-- no drag & drop
-- can't see info you want on screens that you make decisions. 1 examples of many:
---- Research: what did I gain on the last couple of levels of this tech so I can determine if it is worth it to research another level?
2) The AI sucks. No explanation necessary. This is significant because most buyers of a game don't play multiplayer more than single player.
3) There are too many bugs, many of them still crash the game.
4) The "rate" or "pace" of the game seems too slow. SE:IV had it just about perfect to give that "just one more turn" feeling. SEV is far off the mark. Balance Mod is a great improvement, but, no offense, not there yet and still overshadowed by the other issues that can't be currently addressed by modding.
5) There are several game mechanics that are not fun:
-- retreating. A ship with even 1 less movement point can successfully and repeatably keep retreating from superior forces.
-- needing to constantly fiddle with research allocation. I don't know if most people do this, but I do because it bugs the crap out of me to lose research points when you spend more than required on the last level, which you can't know you are at unless you constantly check the data files or memorize them over time. BTW each turn research points change due to construction, happiness, etc.
-- the pathing routine sucks. I'm not sure what the fix is, but the "Stutter Step Dance" illustrates one problem with it nicely:
http://www.shrapnelcommunity.com/thr...1910&Forum=f23
6) A big one for me is not being able to have the game process a turn with the game minimized. Who in SE:IV didn't surf the web or do other things when the game was processing a turn. Not anymore under SEV unless you use crappy winDOHed mode.
7) Having to keep coming back to lists to get things done one at a time. Each time, based on the delay and the reordering, it seems the game recalculates the list. Very tedious. Only the Log remembers where you were at. One example: I'd like to select multiple construction queues and place them on hold with one click, and then later release the holds all at once.
I'm sure you get the idea; I'm not going to rant or make a huge list here, but, taken individually, many of these wouldn't make too much difference, but taken in total, the game just isn't fun.
I will probably upset some people here with the following, but please don't be offended. It appears to me that too much effort was spent making the game super-moddable; so much so that MM either consiously or unconsiously is expecting the modding community to improve the game for him, at least the AI. And this effort took away time from making a fun game. I know that many people find fun in modding and that's great, but it sure looks to me like SEV to date has been more an exercise in making a game
engine, with little to no work on making a
fun game - expecting the fans to make it fun by fiddling with all the modability. I think I personally might have preferred a less moddable game that was fun out of the box. Just my opinion here, folks, please don't take offense.
I know that everyone, myself included, WANTS to love this game and is giving it more than a fair chance. I know that there is every reason to expect that someday after lots of patches and a long time, many of these issues would be fixed. I give great credit to MM for unsurpassed support of games after release.
Bottom line is that SEV is not fun, but everyone mostly agrees that it has the potential to be great. Time spent waiting and dealing with the problems frustrates a lot of people so much that they may be lost forever. And the absolute bottom line is that a game that isn't very fun isn't very profitable.
* steps off of soap box and thanks people for not being offended *