Suikoden V is hands-down the best game in the Suikoden series.
In almost all respects, it beats out the previous best game of the series (Suikoden 2): The story manages to follow the old pattern of "oh I need to flee my home and now I'm leading a band of rebels in a civil war!" but infuses with a lot of new elements: usurpers to the throne, historical wars of succession, threats of foreign invasion. There's a lot of politics involved in this game, and most of the first eight hours are a bit draggy because they spend so much time elaborating on it.
As for gameplay, the trademark Suikoden mechanic comes back again: gathering the 108 stars of destiny to your cause. This has always been the shining point of Suikoden -- the 108 stars quest makes it stand above all other console RPGs where combat is basically the only thing standing between you and the ending. Simply winning all the battles will get you to an ending, but not the ending. To get the canonical ending, Suikoden gives you an additional challenge -- one that is exploratory in nature. Finding (and recruiting) the 108 stars is an incredible challenge, and I ‘m fairly sure that only the most patient of gamers can successfully do it on the first play-through without a walkthrough. Suikoden V feels a bit more difficult than previous games with this regard, as many of the 108 stars of destiny have to be recruited at certain times within a very narrow window only. The closest I've ever come was with Suikoden IV -- I actually got to 107 (!) before missing out on Snowy :/ For Suikoden V, finally surrendering to the fact that I don't have that much time for gaming anymore, I went ahead and used an FAQ to help in the 108 stars, knowing I would not have time for a second play-through.
As for other gameplay mechanics, they're mostly inherited from earlier games in the series, but enhanced to give you more flexibility. I especially like the fact that you can now bring up to 10 characters around with you -- 6 for battle and 4 in the entourage. Any battle-ready characters in the entourage can be swapped in during battle, costing you only a turn and allowing for some interesting tactical decisions. Noncombat characters provide a variety of support skills, such as allowing you to earn more Potch or find more items in battle.
All in all, fifty-or-so hours well spent, even with my limited free time.