My experience and the experiences of the three friends who received invites from me can be summed up as follows.

UI:
3/4 of us struggled with the UI initially, we had issues finding certain features; champion status: where to spend steel for items: being unable to change "orders": thinking there was no way to change orders as there is no key prompt visible for removing a complete order or adding a new one.
2/4 of us were confused via the "loading" screen in which both teams are arrayed against each other as we couldn't see a progress bar and though there was something we needed to press or do at that point. In addition the count down timer sound from 10 to 0 gives you the idea that you can do something, or that you need to lock something in during that time as a it gives a sense of urgency that is not actually there.
4/4 had an issue with the ability to send an invite to another friend via the game's social menu, but you could not accept an invite via the same menu. Making it very annoying for those of us who played with controllers 2/4 as we had to keep switching input devices to do something we felt should be doable with the controller and not the Uplay menu.

Connectivity:
4/4 had issues with either joining a game, or staying within a game, of the roughly 120 games we played either together, in pairs or alone we saw a disconnect in every 2nd game and at least 1 connection issue. Whether it was "synchronizing game state", "re-establishing server connection", "recovering game state" or something else they were far to common to be conducive to good gameplay.
2/4 had issues that sometimes 2-3/4 would connect to a game and the 3rd or 4th would get put in an entirely new game with just bots, while the main group played the original game. At one point I was the bot game player, one of my friends disconnected from her game, joined my game and I error'd to main menu the moment she connected.
4/4 had issues with combat favoring the player with the worst ping. Yet given their wasn't a clear explanation of whether ping was indicative of your connection to the server, or your connection to each other we could never truly tell just how bad it was going to be.
4/4 had issues with the group system. When leaving matchmaking to go back to menu the "quit with group" button never worked. The group leader left the group and another member was given leader and often 2/4 player remained together while 2/4 dropped to their own party. Often the leader disconnected from a game and every group member was pulled out of the game and back to main menu with them. We also found that often we had connection issues upon receiving invites and would often need to restart the client to join a group.

Gameplay:
4/4 of us had issues with the strength of certain actions. The guard-break action in particular when paired with certain character combos often meant that you'd receive two hits instead of one even if the block action was present for the second hit. This we believe was tied to connection as when connections were stable most of us were able to get a block active on the 2nd hit, whereas with poor connection the second almost always made it past our apparently active block.
4/4 had issues with characters that felt like they weren't working as intended, agile characters. Whether this was due to the connectivity issues as they agile characters require good timing to perform their moves, we were unsure.
4/4 had issues with the inability to make mistakes and roll off lethal edges. Shoving or hitting a character off an edge is an interesting mechanic but watching as someone dodges backwards and is stopped by an invisible wall detracts from the experience and doesn't punish mistakes.
3/4 had issues with the massive distances players could close with certain abilities. Either lunging attacks that carried the character 3-4 meters because there was an enemy they were auto-guided into or dodging backwards only to have a character slide/teleport forward and still connect with an attack that should have missed. Swords and weapons as well, either connecting with a player model and nothing happening, or connecting with air and receiving a hit. Whether that relates to connection issues or not we do not know.
4/4 had an issue with how counter-intuitive ladder based combat is. Climbing a ladder was a gamble, 50/50 on whether you or your opponent were knocked off. Standing at the top of the ladder and waiting, there was no issue to kick, or push, only attack the climber and often all that did was injure them slightly. They almost always made it to the top. The one time we saw a player get knocked off a ladder by someone not on the same ladder, it took two power attacks and the ladder player was bugged out and stuck anyway.

Overall:
As a group of beta participants we did have fun, but mostly we struggled to be in the same game together and then when in game we often died to attacks we couldn't see telegraphed thanks to ping discrepancy and then if we made if far enough into the game. We would often disconnect and though the match was enjoyable we'd receive no completion rewards and just be greeted by the many error screens that appeared to make up most of our experience.
As it stands of the 4 players, 3 will not be buying the game in its current state and I personally am on the fence. For a beta this close to release to have connectivity issues of this nature does not bode well for the finished product. That aside I hope any of this is useful to improve the state of the game.