I am 1 stage from finishing this game and can say that Gungnir has really grown on me. It's definitely an acquired taste, though, and I'd say that if you are a fan of SRPGs and are thinking of picking this one up, it'd be best not to try to go into it with any bias or preconceived notions of SRPG gameplay. A few stages in and I quickly realized that to enjoy this game I had to stop comparing it to titles like FFT, Tactics Ogre, Jeanne D'Arc, etc...
In Gungnir, a lot of what I have come to know as standard gameplay mechanics in SRPGs have been turned on their ear: Turn order is handled via "Clock Shift" which initially is a little frustrating to work with because it seems as though your characters practically never get a turn. Once your turn comes up, you must choose which character will act-- if they are able to, based on their "cool down" status from any previous actions. This was slightly frustrating in the beginning because I found myself neglecting certain characters on the field entirely, however, once you start getting the hang of using the clock mechanics and exploiting the system, it becomes infinitely easier to manage.
There is also a mechanic that plays out sort of similar to capture-the-flag wherein during a each battle there are flags scattered on the field which you (and enemies) can land on and "capture", and for each flag you capture it adds a point to your "Tactics Meter", and for each tactics point you have (up to 20) your team receives bonuses such as increased damage, etc... You essentially use a certain number of tactics points for any action you take, and while each action depletes the tactics meter, it recharges over time. This dynamic really adds an extra bit of strategy to consider during every battle as you try to prevent the enemy team from accumulating too many extra tactics points, steal them from you, and combinations of the like.
Also, if you have enough tactics points, you are able to "break" the clock, essentially bumping your turn up. It's not something that's recommended to do frequently, though, as it really depletes your tactics meter, but in a pinch sometimes this can be a real life saver.
Confused yet? Well this will really get you going...
Certain equipment and classes are capable of initiating "Beats" against enemy units during battle. Beats are these super-powered moves that are determined by not only equipment and character class, but unit placement and adjacency. When beats are initiated (again, using tactics points if they are available), other adjacent team members contribute to overall damage/support, sometimes dealing some really massive hurtin' to enemy units. This is by far the most elusive and confusing mechanic in the game to understand, and I still admittedly don't have a total grip on it.
I find the story line to be fairly intriguing, and although it is definitely a linear plot with very little player choice involved, the battles and mechanics are so complex that I am actually quite thankful for this. It is pretty dialogue-heavy, and although you can skip scenes, I think it would really devalue the overall experience. So, if you don't like reading then this might not be for you.
My biggest complaint is with the menu system. Buying gear and equipping it between scenes still remains for me a complete and total nightmare. There is a fair amount of complexity where equipment is concerned (improving it through "alchemy", learning and maximizing abilities, class compatibility, etc...) and the menu system totally screws you here: you can't easily compare items or even see very clearly the stats, and it becomes really aggravating to balance your team as your success in this game is completely dependent on your ability to change things up and adapt to new situations. If you like the game, though, you work around this and deal with it.
Enemy AI is at times brutal. You will decidedly lose some battles. Your characters will get knocked off the map at crucial moments. Some of your characters might even die (perma-death). Your equipment will get broken or stolen. You will be frustrated. But you will also be rewarded, and this is, for me, the hook.
And finally, just as an FYI, I missed this title on PSP and have played it via PSN download on my VIta. It looks great.