siege frigates were much more durable and much less expensive. it was possible to rapidly build large masses of them (like 20) and go kill every planet in your opponent's empire before they could fight back. they have been massively nerfed since then. primarily their cost and fleet logistics have been increased a huge amount.
Long Range frigates of all kinds were slightly cheaper and slightly faster. they had small changes made that increased their cost and decreased their speed. the Illuminator has also had its damage in general increased a little bit, it used to be a lot worse than it is now.
Carriers were very different. TEC and Vasari carriers used to have only 1 squadron. Advent carriers had 2 squadrons. their costs were alot cheaper of course, to reflect this. however, the cost on a per squadron basis was actually alot more expensive than it is now. squadrons themselves also used to be slightly weaker, mostly they were easier to kill with Flaks.
Flaks used to deal more damage to non-squadron ships than they currently do. they were actually used pretty commonly as a counter to Long Range frigates since their combination of cheap cost and high survivability made them an economically feasible counter to LRFs. they no longer are because they no longer deal enough damage to non-squadrons.
capital ship abilities were pretty different. i don't think i remember all of them, but here are the highlights.
Malice did not have a target cap and i think it applied damage in real time, or by some other means than it does now. it could be easily combined with Cleansing Brilliance (on the Radiance ship) to instantly deal multiple thousands of damage to every ship in the enemy fleet. it was very nearly a one shot fleet kill.
the explosions resulting from ships dying under Volatile Nanites had a much larger area of effect and it was possible to set off gigantic chain reactions with this by killing just 2 or 3 ships. the rest of the fleet would blow up instantly in the chain reaction explosion. also pretty close to a one-shot fleet kill.
the Marza's missile barrage was bugged and not working properly. it wouldn't fire all 20 waves, and would sometimes drop targets for no reason. nobody used it because it was broken. the Marza was only ever used for Raze Planet back then.
Embargo on the Sova was slightly more powerful. it had cooldown=duration at all levels (now it only reaches that at level 3) so it could be on constantly even from a Level 1 Sova. it also had a lower antimatter cost. this led to alot of people using their Level 1 Sovas to rush the enemy homeworld at the beginning of the game and completely cripple their economy.
also, the single player AI in 1.0 was basically non-functional. it used to run away from every fight no matter what. it also used to build almost nothing but siege frigates. there was a gigantic update to the AI in 1.04 i think that made it much more fun to play against.