4 and 5 are somewhat divisive for a lot of series fans (4 in particular, by what I've seen), but as someone who likes the series but is by no means a die hard, I found both to be worth a go.

The revamped battle system is really good fun (though so, so easy to break, especially with Raquel in 4... :'D), and the platforming / side scrolling elements are a good fit for the series, and somewhat make amends for the less interesting puzzles. Story in 4 gets a bit stupid as it goes on (though there are a couple of characters I liked!), but it doesn't veer into painfully bad territory, and is still reasonably enjoyable if you can turn off your brain. :'D And I quite liked the story and characters of 5, copious anime tropes and all.

Music is also great as always, particularly 5's soundtrack, which has a couple of really killer battle and boss themes. <3 They're not top tier PS2 JRPGs by any means, and I probably prefer 1-3, but don't go in with super-high expectations and you'll probably have fun if you like that kind of game.
I also thought both were quite pretty for middling budget PS2 RPGs (though I missed the cel-shaded models of 3), and 4 in particular had a couple of environments that I remember really liking the look of back in the day.
