Renegades is the predecessor to Mercenary. (Actually, the evolution was Renegades - Legends - Mercenary). The games are pretty similar, though. Mercenary adds new ship frames, gas giants, a whole lot of new equipment options, the ability to build stations and improved multiplayer code, but (as of now) doesn't allow you to mod the universe anymore.

Both games are sandboxes, there is a campaign/quest chain, but it's presentation is pretty lacklustre. Evochrons main selling points are the multiplayer mode and the seamless planetary transitions, and to a lesser degree the ship customization. Exploration is pretty weak (there are dozens of hidden star system, but you basically have to stumble blindly across them or do a rather unfun pattern search - and even if you find one of those systems, it's just "more of the same"), and most of the mapped star systems are rather small. The starting system is a noteable exception, but some of the other mapped systems simply consist of a sun and two planets with little inbetween.

The basics are there, the random missions can be fun, but IMHO it needs a bit more game and less simulation to it. Once you've done all the mission types and tried all the frames, there's precious little to keep you playing. Mercenary adds multiplayer with persistent servers, but from experience most of them get pretty cluttered with pointless stations as building them is dirt cheap, and removing them requires a special one-shot item that costs about 20 times as much as building a new station. Do the math.

If you want to get a game from the series, grab Mercenary, it's definitely the most polished of them, but don't expect the second coming of Elite. The games are quite nice and I appreciate the effort of the one-man-development team, but they lack long-term motivation. You've seen all there is to see pretty quickly, and there's little besides PVP to keep you coming back.

-Blackthorne