As someone who has played Ace of Spades for way too long, let me introduce the history of it to you first:
In April 2011, somebody called Ben Aksoy released a pretty decent and free FPS with voxel mechanics called Ace of Spades. This was a game that people mostly played on a randomly-generated map similar to Minecraft's randomly-generated maps (only without the trees, only grass, some rivers and more hills). The default and only gamemode at the time was Capture The Flag. All of these in combination allowed for some fun gameplay that required some strategy. Dig tunnels to capture the enemy's intel, or build a fort to defend your own intel. Every man only had a rifle, spade, grenades and some blocks (unlike most FPSes there were no newby spray-and-pray weapons).
As this game rised in popularity, a certain company called Jagex was interested in purchasing Ace of Spades. As Ben needed some money to keep updating his game, he agreed. At first, Jagex kept this a secret as to not interfere with the growing progress of the game, and its community with all of the mods/maps/gamemodes/scripts that they were producing.
And so the game kept updating, but since Jagex's buyout of the game the direction of Ace of Spades had taken a different turn from the old trench-warfare, stragetical FPS it was to a more typical, faster-paced, almost Call of Duty like FPS (SMGs and Shotguns were added, sprinting added, etc). Coupled with new maps such as Hallway and Pinpoint which abondoned some of Ace of Spades' most important features (Hallway doesn't allow you to build a tunnel underground, people usually battle in a very narrow hallway just a few blocks wide, and it's quite easy to just spawncamp if you're at the top, Pinpoint does not allow any tunnels at all, and the whole map is at the same height), and Ace of Spades became not much more than a free Call of Duty + Minecraft game.
And then without much warning, development on Ace of Spades almost halted. Only 1 new version was made that was a beta and was not approved to be an update to the main version of Ace of Spades. And then Jagex had announced that Ace of Spades was to be scrapped to make way for their version of Ace of Spades, almost a completely new game, pretty much alienating almost all of the current Ace of Spades community at that time. At first Jagex's Ace of Spades had some popularity, but as people realised how much the game just sucked in general (lack of timely updates, bugs and glitches, game-balancing issues, etc), and the fact that the game was made by Jagex itself (Jagex do not really have the best reputation of a game company) led to the downfall of the game. Although there have been a few great updates (Classic CTF update, Map Editor update, KV6 modding update), it still doesn't excuse the lack of timely updates, especially if almost all if not all of them brought along some bad features or some bugs.
The new Ace of Spades turned that CoD aspect all the way up to 11, and added some Team Fortress 2 into the mix (while Team Fortress 2 is a very good game by itself, the way it was implemented wasn't). Stuff like Rocket Launchers, Jetpacks, classes were introduced. While some fun could be had in this new game (especially the '30s Gangster game modes, and Classic CTF), it was mostly just a mess. In a typical Ace of Spades match it would not be suprising for you to be accused of "hacking" and getting votekicked for it, people griefing away every block that you build, a lot of spawncamping (but which since has been reduced with a new update that added and changed spawn positions) and just a lot of kids who play the game in general.
If you really want to buy this game, buy it on a seasonal Steam Sale (Ace of Spades usually, if not always are one of the games that is affected by the sales). Classic CTF (basically what Ace of Spades was before the SMG and Shotgun were added and before the game approached a faster-paced gameplay but with better graphics) and the '30s Gangster game modes (VIP, Territory Control) are really the only modes worth playing, maybe with the occasional normal CTF and Diamond Mine too. You should stay away from playing TDM or Zombies (these are the 2 gamemodes which suck the most, and where most of the kids are at in Ace of Spades).
Otherwise if you're not willing to pay, you can try the classic, free version of Ace of Spades at buildandshoot.com,
if you like the same, crappy overplayed maps (Hallway, Pinpoint), spray and pray SMGs, playing with a lot of Brazillians who don't speak a single letter of English and people who need to use aimbots/wallhacks to play well.
TL;DR: Both the Jagex's Ace of Spades and the "classic", free version of Ace of Spades that can be found at Build & Shoot suck, but suprisingly it's the Jagex version that sucks less, because at least it has some kind of variety in gameplay.