It's basically a 4X-like RTS game.  It's a great game and online multiplayer is very challenging and the strategy is deep.  However, very sadly, the game has a small online player base in spite of its sales.  During North American and European prime time you can sometimes find 100 people playing it online.  At other times there might only be 40 or 50 people online and at other times fewer than 15.  There isn't any real clan activity, leagues, or competition as a result of its having such a small player base.  Also, consequently, few custom mods are played online (at least at the official Ironclad Online server) and custom maps do not auto-download, so there really isn't a custom maps or mods scene.

However, it's still a great game if you enjoy intense, challenging online multiplayer and strategy.  Once you start playing the game you won't pay too much attention to the graphics and you'll spend almost all of your time zoomed out managing the movements and attacks of groups of ship icons.  (The review videos always show the pretty ship closeups which you almost never have time to watch in a game, nor could you manage your fleets and ships intelligibly at that level.)  The reviews rarely show views of the full gravity-well-battlefield zoom view level, which is the view you would use to fight battles.  At that level of zoom your ships appear as icons.  (IMHO, most of the video reviewers are complete noobs who don't realize that the game will be played at that level of zoom.)  The close-up graphics are fine IMHO but I never get to pay much attention to them.

Have you considered playing a demo?  To get a sense of the kind of strategic issues that are involved, you might browse the Strategy forum.  One of the common complaints about the game is that they take too long to play online (which isn't a problem for many people).  A 3v3 on the large random single star map is normally decided by 1.5 hours and normally over within 2 hours and a 4v4 on the huge random single star map is normally over within 2 to 2.5 hours.  Is that too long?  You decide.

SOASE is not only fun in multiplayer. In fact, I never play online multiplayer. I just do skirmishes. The AI is challenging and games are never the same way twice. Another RTS you might want to try is Supreme Commander.

Samurye.

Yeah, the online player counts are depressing but you can normally find a game to play (or start one yourself and have it fill) if you aren't too picky and if you're patient.

Note that there are also people who play the game over Hamachi virtual private LAN, but many of them may be pirates and many aren't playing with the most recent patch.  I think the Seven Deadly Sins (mod) community plays over Hamachi.