If you liked Final Fantasy 7, there is almost no reason why you shouldn't like 9; the two are VERY similar games running on the same formula for the plot; plus 9 has a lot of treats for longtime fans of the series.
Final Fantasy 10, I won't spoil anything for you, but for me it was the opposite, I felt the most interesting parts of the game were in the last 30-40% of it. The story to that point is fairly unspectacular, but the character development I do like all the way through the game; the great characters make up for the plot. If you are complaining about battles being easy now, you won't be in the very near future. I also really like Rikku, she's my second favourite character in the game next to Wakka. Another one of my favourite RPG's, Earthbound, doesn't have a spectacular story either. I tend to look at different elements in different games. As far as characters go, I feel that FF10 is among the best of any game made yet so far. It's not just that element either, it is the adventure which occurs throughout the game. A lot of people were hard on the games music as well, but I felt that some of the best songs in the Final Fantasy series were in that game. The piano song at the beginning "To Zanarkand" is in my opinion, one of the best songs ever composed for the series.
Anyways, if you stop playing right now, you will not understand why Rikku is there at all, it is revealed in the game. You just haven't played long enough.
Also, for Final Fantasy 8, it's not too difficult to figure out. There are a lot more plot details that you have to pay attention to in Final Fantasy 8 than other FF games, that is why it is my favourite. In short: Ultimecia is trying to get ahold of two people, Ellone and Adel. Ultimecia is able to absorb the power of sorceresses into her, she does not yet have the power of Adel, this is why she wants Adel. Adel was lost from history during Laguna's time. A time machine was created using data extracted from Ellone which allowed Ultimecia's consciousness to travel to the past back to the time of the machines creation, which was before Squall's story begins, she had possessed Edea (which is found out on disc 3). Edea, a sorceress, created SeeD, an elite military organization which uses GF's, to defeat the Sorceress from the future (Ultimecia); in the game's ending, it is revealed as to why she did this. Anyways, Ultimecia still had not travelled back far enough in time, Adel had already vanished by this time. Ultimecia required Ellone in order to go back even further in time to the period which Adel was still alive, Ellone herself has the powers to send peoples' consciousness' back in time. If Ultimecia was able to locate Adel, and take control of her, she could unite the two's power into one, essentially making her God.
Think of the movie Highlander, the world began with a ton of immortals, each time one is slain, his/her power is absorbed by the slayer. It is the same with the Sorceress lineage. It began when Humans defeated the God Hyne. Hyne split his powers up among chosen ones, most were female. The chosen ones, upon death, passed their power onto a successor; by Adel's time, there were only two sorceresses left. Adel dissappeared from history, leaving only one, and there was a large missing chunk of sorceress power lost from the world.
As far as the plot for FF games go, they were never realistic, that's what I enjoy about them. None of the Final Fantasy games are even close to realistic. About some games being at their best towards the beginning, I felt that for Final Fantasy 7 and 9 only; the rest of the games I felt were reasonably solid all the way through, FF8's best part is clearly disk #4 though, but you really need an understanding of the rest of the game to get the full impact of it. The ending of 8 is absolutely amazing, I think many will agree that it is at the very least, one of the top 3 best RPG endings of all time to this date; it is easily by far my favourite. There is no other ending in the FF series which carries so much significance as that one.
My favourite FF games are FFIII, FF8, and FF10. I asolutely love those three games. I do not think you should judge a game until you finish it, because from what you played of Final Fantasy 8 and 10, you are complaining about story sections lacking in the game which exist in the portions that you did not even play.
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