I currently play on TOUGH, but my first game was on NORMAL. I haven't tried harder diffs, only because i never play in maps smaller than large, so my games take a LONG time to finish, and I do have to work full-time for a living.

I have some issues with game difficulty, but the AI improves on every patch, so I'm not that worried.

Though I play a bit more on the diplomatic side of things...

For me, Crippling ( Genius ) remains the best challenge/fun ratio with a 120% economic bonuses to the AI. It's not that the Incredible AI ( ultimate level ) becomes too clever, no; but competing against 200% economic cheats is no fun at all.

I usually play at normal I can win at tough but only threw tech of alliance victory which is no fun

My last couple dozen games have all been Tough difficulty. I agree with the "planet building" comments..while much better, there's just too many costly mistakes (or the planet is changed incorrectly to combat difficult situations).

I've lost two games due to the most horrible starting positions. Most of the wins were decided by mid-game and only a couple were undecided going into the last year.

I'm getting near mid-game on my first Painful attempt. If the Terrans ever learned to expand during the planet grab phase, us non-evil races would have a much easier time because the Terrans wouldn't always get absorbed by mid-game. ...Otherwise things are going decently, but eventually the Yor (Terran eaters) will attack if only because they already have twice the production ability of anyone else. (note: Drath have built several influence starbases and have never upgraded them).

Short version: I already notice a distinct difference between painful and tough. Nothing insurmountable, but definately a lot less room for error.

Disclaimer: I like a feeling of space and distance (just doesn't make any sense for every sector to have a dozen habitable planets) so I play with abundant habitable planets, but common number of systems, tight clusters and Gigantic map with 3-4 opponents. That way you still have to research techs to travel distances and there's plenty of resources (~110-130 planets between 4-5 races)to go around). Also, I've turned on the CPU intensive AI's.

I started on normal. But I recently switched to painful. I am currently in the middle because I like large games alot more than anything smaller. and I have to restart a few times, because it always seems that my system is located real far away from any other system.

well, i actually started on cake walk, just to get a sense of how things work w/o worrying about the AI players.

moved right up to normal for a game, then tough.

now i play crippling or maso. i usually play abund/common/uncommon for the star and planet settings, tight or loose clusters, abundant anomolies, and research usually on very slow. usually play with 9 or 7 opponents. i only play with blind exploration if i use loose clusters; otherwise, it's too likely that 1 player ends up in the corner with only 3 planets.

crippling gives me the best challenge i can still reliably beat. sometimes in maso i'm playing games with a strong disadvantage. sometimes i like that, sometimes it's kind of fun to give it my best and still lose. above maso i have increasing difficulty. i can still win, but it usually is only through tactics i don't totally like (selling opponents ships that make them weaker against you, stationing ships next to mining bases and then giving the ships to the base's owner's opponent so that the base is destroyed. those are good ways to win, but i prefer having fun and have more fun when i feel immersed.

lately i've been playing mods more than anything. i took the example mod and removed the new races, new UI, and slimmed down tech tree. i added a couple new techs (most notably a line of medical techs that boost pop growth) and other things. also tried to 'help out' some of the typically weaker players (i don't think i've played any un-modded games where the iconians were a significant threat).

your miliage and preferences may vary, or course. if you want to try and go to a higher difficulty level, a good thing to do is give yourself some 'training wheels' by modding in some nice bonuses for your race of choice.

I have settled in on crippling,

I like military conquests.
It seems to me that with suicidal or obscene, you need to go the wimpy way and flip planets.

Suicidal! But unlike Vulcan2, military is the only way I can win.

Started out playing on normal/large and won pretty easily. Last win was on tough/gigantic and was challenged by the AI in pace, but beat the AI with some margin in conquest. I'll try painful next game. May get beat a few times before I can score a win on that level. May have to go back to tough. We'll see.

I've played 3 games all on gigantic maps with 9 opponents. Regenerated maps
each time till i got a homeworld with tile bonus's of my liking.
1st game was tough level and was easy, 2nd game was painful level and even easier ( i improved my tacticts ). 3rd game was suicidal level and was a good
fun challenging game.
From what i see, the tile bonus's on your homeworld have a lot to do with what difficulty level will be a good game. Just so much depends on your homeworld for the first 100 or so moves. I have no doubt that without almost
ideal tile bonus's, my strategy wouldn't work on the suicidal level. However,
I do see possibilities for other strategies to have a chance -- but pretty slim chance.

The first level where I get any challenge at all is the aptly named challenging level. Not very difficult and the games I play at this level are decided well before I'm out of the mid-game point.

Next Game I'll ramp up the level a notch and see what happens