I originally played the first two games through RealArcade. I've just started the third game, so I can't speak too much about it or the rest of the series. But I can confidently assert that the series is worth getting, if only for the first and second game. One thing I've always disliked about the fantasy "genre" is that many of the works based on it are derivative of Tolkien's lore but don't build on it in any creative way. Geneforge eschews all that, focusing not on the binary struggle between light and dark (and light and dark races), but rather on the grey struggle between privileged creators, their creations, and the unprivileged non-creators. The games cover the rebellion against the Shapers from its beginning to its end. There are many factions to join and spurn, and with the exception of the fifth game, you can complete the game as a mass-murderer killing everyone indiscriminately if you wish. In the first three games, you start as a Shaper apprentice and have the choice of three classes. Shapers are strong in shaping but weak in melee combat. Guardians are strong in melee combat but weak in spell-casting. Agents are strong in spell-casting but weak in shaping. The fourth game gives you the option of starting off as a rebel, with identical classes and two new ones exclusive to the rebels: Shock Troopers, strong in shaping but weak in spell-casting, and Serviles, creations strong in melee combat but weak in shaping. Geneforge 5 adds a sixth rebel class, the Sorceress, strong in spell-casting but weak in melee combat. Combat is turn-based. If you invest in a little intelligence in your creations, you can manually control them. You can also control your human party members in Geneforge 3. Combat isn't all there is, though--there's lots of lock-picking (mechanics skill) and persuading (leadership skill). It's unwise to not invest in those two skills, unless you plan on just killing everything in sight. The only gripe I have about the game mechanics is the lack of user configuration. You can move the camera only with the arrow keys, and you can't really play in a window. This only applies to the first three games, I'm not familiar with the preference settings of the fourth and fifth games. The biggest shortcoming of the series is its look. The still images of the start menu and cutscenes are all right, but the rest of the game just isn't very pretty. It doesn't have a unified art style, characters don't have unique designs aside from different colour palettes, there are very few animations, and the animations are often very awkward and laughable. For the most part, everything is static. It just doesn't do justice to how fleshed-out the world really is.
