Personally, I think the original Master of Orion is highly underrated by the TBS community. MOO was much simpler in some ways, with planets controlled by simple sliders (allocate spending to research, industry, ship-building, defensive structures or ecology/population). Technological research was handled similarly with spending allocated to six or so different tech fields (Computers, Weapons, Propulsion, etc). Ships were sent from star to star (no "solar systems" or hanging out in deep space), and you were limited to six different ship designs at once (which meant that once you wanted to build ships of a seventh class, you had do scrap all the ships of one of your current designs). And of course there was the guarded planet Orion.
There were a few things that make this my favorite strategy game of all time. The research tree was randomized so that each race had access to roughly half of the technologies in the game, differing each game. This made research and diplomacy more interesting, since you couldn't follow the same path every time, and sometimes had to trade for choice technologies. Also, each tech field had inherant effects as you researched them (for example, research in construction had the secondary effect of making your ships roomier).
The ship design was enhanced by the fact that you couldn't custom-build every ship in your fleet, but had to build designs that were worth one of your six design slots. Nor could you simply start building new ships every time you got a new tech, unless you liked scrapping your tiny fleet every time you discovered a new gun. Further fun came from the fact that there were many trade-offs in ship design, such as whether to build lots of small ships, a few big ships, or mix it up. Big ships required more space dedicated to engines, so you usually had to use older technology engines on them. Technology matured as you researched relevant fields, so you had to decide whether using your newest weapons and engines was worth all the extra space, compared to your tried and true toys from a few tech levels back. And there were several components to balance. After all that, you threw them into combat on a small 2-D grid and fought it out against the enemy. Simple but effective.
Each race had its own personality, with some variations. This was fleshed out by diplomatic tendencies, race-specific bonuses, and unique costs to research certain fields (so a certain race might get a discount on Propulsion technology). Plus the diplomacy was interesting enough, with a variety of options, and a simple but compelling spy-counterspy component of trying to decide how much spying was enough (with the option to go for espionage or sabotage).
A lot of people seem to disagree, but I think MOO was a lot more fun than MOO2. It seemed to have a lot of strategy, that was only enhanced by the fact that you didn't spend any superfluous time mucking around with planetary management (just enough to decide priorities, no "build queues" or anything). Even w/o any civ-style buildings, MOO1's planet management was more interesting than GalCiv's, which looks to be remedied with GalCiv2. I only wish I could get the thing to run in WinXP.
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My main opponent were Darloks. For most of the game I kept counter-espionage slider above 30, using about 15% GDP for that 
. When the war broke out, I still got some fac's and missile bases destroyed, but only small numbers.
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