Both "Umi ga Kikoeru" and "Mimi wo Sumaseba" created on Studio Ghibli, but both movies not directed by Miyazaki. Both - good romantic stories, but in "Ocean Waves" more older MC. Both shows a real places in Japan. Precisely shows. Sometimes even photographically exactly. Both left in the soul a feeling of quiet melancholy and good feelings after watching.
Both stories contain a girl who find the school that they are in boring and is of no real challenge to them. Rikako Muto and Haruhi are amazing in sports and in studies and are considered the 'perfect girl' for any guy but are really hard to come close to. They also have an air of arrogance which other school student notice and dislike to an extent of being jealous of them. They both eventually meet an average guys whose within thier same year that don't really have interest towards them but soon find a deep profound love for each other without realizing it.
Ocean Waves has a more mild and believable Tsundere lead who ropes in a similarly earnest guy, with the same context of high school melodrama and family problems. While these essential elements are the same, the plot and the characters are aimed at a completely different target audience.
It's not a sure bet that Ocean Waves will be to your liking just because you enjoyed Toradora, but it provides an interesting and more realistic look at a tsundere romance that's worth checking out.
The first half of TPPiOED is a lot like Ocean Waves. There's a love triangle, where two guys (one with glasses, one not) get involved with a girl. The girls in both differ greatly, Ocean Waves' being very selfish, but you'll watch both and have similar feelings.
Unlike TPPiOED, Ocean Waves doesn't turn into a sci-fi mess half-way through. That's why I rate Ocean Waves a lot higher.
In terms of other Ghibli titles, Ocean Waves is very similar in execution and 'feel' to Only Yesterday and Whisper of the Heart; two of the more mature Ghibli releases.