As a founder, I've had access to these Mercs for a while now and have started and played towards near the middle game (Large vs 7 AI, Incredible). This has given me a chance to use and develop an opinion of Mercs. In the right circumstances they can be helpful and useful especially early in the game.
For example, one game I the early multi-sensor ship that I buy (hint..buy a cargo shell and upgrade next turn is way cheaper) noticed a nearby PC relic and also many anomalies above me that I couldn't quickly reach with my survey ship that had gone below me. Therefore, I spent 750 to buy a Merc survey ship. Soon, each survey ship had attacked a protected graveyard and now I had found two nicely shielded ships. These slowly moved to the PC relic and along with one of the survey ships, I took the relic (losing my 2 shielded ships) and now had a nice cash infusion and 5 Elerium. Hmm..time to buy a Merc but the killer beam ship needed another resource and no AI had it yet so I slowed my colony rush plans to build a constructor.
Soon that Beam Merc was making a mess out of the Iconians, destroying their constructors, colony ships and whatever. I then rushed towards PI and took their planets before they could fend me off. Fun, YES!..OP ..perhaps, but this isn't something that you can do every game. However, in some other games, I've had no use for early Mercs that could justify paying for one.
So, Mercs add a new dimension to the game and add some new strategy as well. GC3 is a better game with Mercs than without.
Mercenaries indeed is a step towards making GC3 as great a game as GC2 is, but there's lots more to be done.
Here's a few of my thoughts as how to improve the player's experience with Mercs.
1) They need to be upgradeable!! One should be able to upgrade them for the same as it would cost if upgrading the same ship that was not a Merc. The Merc then would lose all its special capabilities, if any.
2) Late game Mercs cost too many resources for the most part and aren't good enough.
3) I strongly dislike any cost increases as time passes.
4) I'd like to see one or two more Mercs available initially that just cost credits and cost no resources.
In closing, I'll again state that I find this to be a better game with Mercs than without.
.. neilkaz ..