I loved the original EE, it's probably my favourite RTS. The campaigns were nice and varied, but I always found the scenario editor to be the most fun.
You could set up some interesting games, limiting what units and buildings could be made, what population each individual faction had, starting resources and even what age they could advance to. Plus it was easy to alter terrain and add things in. I always had good fun setting myself an age or so ahead of the AI, but then fighting 15 of them at the same time. As mentioned though, the AI can be a little funny in this game. It will either be a nightmare, expanding quickly and building plenty of defences whilst also being a constant threat. Or it will expand aimlessly, placing walls in silly places and trying to storm you with a single type of unit.
The sequels I never got on with, EE2 was decent but I never put much time into it. EE3 from all reports at the time was a massive disappointment and killed the series. The first two might not be as good as other games of that genre, but they're not bad games by any means, you can still have plenty of fun with them.