I'm so confused by the fact there was actually about 3 pages of discussion about a card that's just a very bad counter.
Think of this: is it much worse at countering than
Calculated Dismissal? Yes it is. Do we use Calculated Dismissal. No we don't.
Lunar Force is by far the most underrated card of the set so far. So many people bashing at it without even thinking about it. "Oh it's a worse counterspell for 3" "Oh people can choose what will be countered". Seriously, are you guys this basic? Geez... The card's not supposed to be compared to Cancel, it's completely different, it brings new things to the table, and you're all just ignoring it. Ok, so I play this turn 3; pass on to you; now you have to deal with it, cause if you don't, it basically turns into a free counter later when I have my mana open again and this is still on the field. Now, how do you deal with it? Will you play some card you didn't intend to just to get this out of the way? Will it mess up your curve? Probably. If you weren't going to play something that turn anyway, fine, I just got a "free" counter later on, which would not happen if I just had saved Cancel in my hand and you eneded up not playing anything. Another thing people are forgeting it's that once it enters the battlefield it turns into an UNCOUNTERABLE Cancel, because once it triggers it's a triggered ability, not a spell. It forces the opponent to play around it, it looks super fun to play with, and I'm definitely going to try it out if it makes into Duels. Good luck dealing with it then, haters.
IMO, unless you can recur it, it is not worth it.
A couple of drawbacks besides the obvious.
First, you can only play one at a time. 2 or more on the battlefield are wasted.
Second, some spells will trigger it but not be countered. And example it Exquisite Firecraft. It may not be that common, but still an issue.
Third, it lets the opponent get rid of cards that have no use. This may be a more rare case, but as example, I run a creature less deck, and that blanks all creature removal. All of a sudden, my opponent can cast Declaration in Stone on his own creature and expend Lunar Force.
Now, I think there may be a deck out there that can use this card. A deck with Emeria would be one I would think it would work well with.....but then again, Emeria works well with many decks if you can get her out and keep her out. This could give her some added protection, but IMO, a deck will kind of need to be built around Lunar Force to make it effective, and I don't think we have enough to make that deck effective.