My following statements are going to focus solely from an MP perspective...if that is all that you really care about, then hopefully this will help you...
While Rebellion is standalone, it is in fact the 3rd expansion of Sins (with Entrenchment and Diplomacy being the other two)...titles under the publisher/developer Stardock (it's not quite clear what their exact role is) have a notorious history of game balance issues and weak multiplayer...I am referring to the Galactic Civilization franchise, Sins of a Solar Empire and its expansions, and Elemental...that being said, Rebellion is significantly improving with each update and it is possible that after more updates, the balance will be really good...there is, however, no guarantee, and I can only point to Stardock's history...they support their games for long periods of time, but their ability to balance a game for competitive MP is questionable at best....
That being said, I by no means would call these games bad....they are awesome games, but if you are reallly only looking for a competitive multiplayer atmosphere, sins might not be the best game to go for...while Sins may have more potential as an MP game, the devs actually focus more on the SP aspects...the MP community is stronger now that it probably ever has been, but it is by no means large...furthermore, there is no ranking or matchmaking, and likely never will be...
There are several things holding back Sins from having the true competitive MP atmosphere that you probably are looking for:
- Random map issues - there are few fixed maps with any level of popularity, so most games are on random maps...this of course leads to situations where player starts can severely affect or even decide the outcome of the game....even with fixed maps, random elements like militia counts and extractor counts can make seemingly balanced maps ridiculously unfair...
- Nature of typical games - due to the size and culture of the community, the most common games are either friends doing comp-stomps or large team games (4v4s or 5v5s)...obviously the comp stomps don't add any sense of competitive MP, and the large team games make win-loss records completely meaningless...games are often decided by player drops or stacked teams rather than by your individual skill...still, MP can be lots of fun, but if stats and records mean a lot to you then Sins is probably not a good match...
- Lack of MP support - it is highly unlikely that matchmaking or a ladder system or rankings of any kind will ever find themselves into Sins...the small community, the random map issues, and the nature of most games would make such MP additions meaningless...furthermore, MP support isn't a significant concern of the devs...
- Quality of servers - Lag, for a variety of reasons, is a big problem...the nature of the game engine combined with the servers makes late game lag unbearable in many cases...for some, it gets to the point that you practically can't even give move orders or properly micro units...I've even had to hard shutdown my game via task manager because I couldn't get the menu to come up
There are a lot of great aspects of Sins...the effects are great, the gameplay is pretty cool, and it's the perfect game for casual MP with some friends...Sins also has significant modding potential and the community provides a lot of support and expertise in that area...unfortunately, if competitive MP is the only thing appealing to you, I don't know if this is a good match...
Instead of just dismissing Sins Rebellion entirely though, I'd strongly consider tracking the game...you never know, the balance might actually get really good and the MP community might get more organized...
As for the specific concern of unit spamming, I find that the entire focus of competive games really is titans...it is all about the titan...it is about rushing the titan, yoinking or killing someone else's titan, leveling your titan, preventing the other titan from getting fed XP...fleet compositions are all about supporting the titan, killing the other titan, countering the titan killing fleet, etc etc...
Bomber spam (and it's counter, fighter spam) is basically the norm...certain titans will also lead to LRF spam, HC spam, or flak spam...there isn't just 2 units that get spammed by everyone, but you'll find that more successful fleets will often rely on spamming 2 units together (for example, fighters and HCs or bombers and flak or carriers in general and LRFs)...regardless of what you spam, once high level titans come on the battlefield, anything other than a starbase, carrier, or capital ship is virtually negligible with few exceptions...however, the early game counter system is much more interesting and improved over that from diplomacy....
As an FYI, Trinity is a repackaging of Sins and it's first 2 expansions....Diplomacy (the 2nd expansion) actually came out in february 2010, and the last update for it (v1.34) came out more than 2 years later...
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. It looks awesome, i like the gameplay, i like that there are now new strategies to battles and that devs are constantly upgrading it with updates and balancing it. I think that the steam integration really helps with the multiplayer.