Space Empires IV is like a truly complex, four course meal. The flavors are nuanced, will challenge the faint of heart, and if you trust the chef and stick with it to the end, is truly satisfying.
I spent hundreds of hours on the predecessor to SEIV, and the terrible graphics but amazing gameplay of SEIII will live in my memory forever. Space Empires IV is a worthy successor. Unlike some sequels, SEIV builds on what made SEIII great, preserving the best features and adding lovingly rendered graphics, enhanced ship design features, more technologies, bigger galaxies, better AI (although this is probably the greatest weakness of the series), and more.
If you've never played 4X games before, SEIV is a heavy entry title. It does have a steep learning curve, and only those who truly love micromanagement will ever appreciate the deep complexity at the core of this title. It's possible to play without getting bogged down in the details as a variety of assistants can be turned on to help manage minutia like build queues, research, and the like. I'm not that familiar with them as I never play with them on, but I'd imagine they would help if you're just getting in to the game.
The real brilliance of SEIV is the extensive technology tree and the infinite variations in how it can be applied. Over the many hours I've spent with this game, I've tried countless variations on technology applications, and there is no one true path to victory. Many exist, they are all fun, and contribute greatly to the near-infinite replayability of this title.
When you get tired of the base game, the second greatest feature of SEIV kicks in -- it's very open to modding, and a strong community of modders exists for the game, with simple mods like technology tree augmentations to extensive mods like Star Wars or Star Trek "mode" mods. Whatever you want, it either exists or wouldn't be hard to make.
Needless to say, I'm a big fan of this game. If you're new to 4X games, you might want to come back to this one after getting into the genre a bit more. If you're a 4X pro and want to embrace a true challenge -- this is the game for you.