It seems to me sixth edition is very much a dice game this time around. I don't have a problem with that aspect and I've had a lot of exciting games in sixth edition that came down to the last few rolls of the dice. I am in a phase now where I like to play armies that are exciting versus fielding armies that are designed to beat the meta. I don't think there is a real meta anymore with allies and how the missions work now. Necrons Grey Knights were my first solid winning army for sixth edition - I don't think anyone can honestly deny that is a competitive combination. I learned how to play sixth edition competitively with Grey Knights starting with Draigowing. It finally got boring just like any army you win a lot with over the course of time.
A lot of new codices are rolling out now... More so than ever before since I can remember and that also breaks the meta. To a large degree you don't know what to expect. An army that is strong today could be weak in a month or two. I've seen it happen before and it kind of sucks for new armies that have a short shelf life in terms of being competitive. It happened to both Blood Angels and Dark Eldar. GW gives and takes.
The best armies now are the most balanced... They excel in all three phases of the game - movement, shooting and assault. If an army is weak in any one phase it can be made to suffer. Movement is still the strongest phase and the least dependent upon the dice. That is one reason why I think the new eldar could be very strong, even stronger than the new Tau. Tau are really good at shooting and that's it. Figure out how to assault them effectively and they will fold. For example Tau have Fire Support to enhance their Overwatch so you assault them with multiple units and first send in a sacrificial unit to absorb their super fire power.
My army I'm playing now needs some good luck to win. If I can assault out of two land raiders on the second turn it's lights out... Otherwise it's going to be tough and Emperor forbid any armies that can easily pop AV14. It's tough to lose for just about anyone but it is not the end of the universe either. I could have focused on building a competitive Tau Grey Knight army but I'd rather work on my World Eaters. One thing I can say for certain in regards to new Tau Grey Knights army... If you're relying on a Strike squad to provide your muscle you're going to eventually lose. Sure a Strike squad has a lot of force weapons but other than that for the most part they are an expensive tactical squad. They have some good things but they are weak in melee versus most any dedicated close combat unit.
So like I said sure it's not fun to lose for the most part but then again nobody wins every game either. If you're not winning enough to your satisfaction maybe it's time to start playing a new list. You don't even have to change codices - try some new units. For example I started out playing Grey Knights as the primary detachment with Necrons as the ally. They did okay then I switched out using Necrons as the primary detachment and I started to win more games. It worked for me and I'm sure it can work for you too.