the oracle games don't try many new things, insisting instead on celebrating zelda.
after majora's mask two handheld zeldas were developed by capcom, but only came out about a year after MM, so they were probably developed alongside MM, gaining access to its storyline.
the oracle games continue link's musical, time-travelling career but in what seems to be another flourish of japanese-ism, they also give him the ability to change the seasons of spring, summer, autumn, and winter.
both of the oracle games borrow heavily from link's awkening, taking most of that games sprites and tiles, and 'colouring them in'. link's awakening was the begining of the zelda formula, and the oracle games are the most formulaic of the bunch, borrowing so heavily from the two N64 games that it struggles to find its own identity (just like kirby).
let's see now...the cuckoo lady from ocarina is there, the crazy windmill man, tingle, the gorons, the possibly gay postman, the happy mask salesman, din/farore/nayru, the deku tree (oh sorry, the 'maku' tree), and a bunch more besides. i actually like to think the oracle games are more of a 'celebration of zelda', because four swords adventures does the same thing, paying tribute to LttP in particular. i don't know....i used to like them, but playing them again, 7 years later has made me realize what they really are.
the characters aren't the only things that are borrowed. link visits the usual locations: spooky graveyards, mountains, grassy areas, lakes etc. the oracle games also borrow from the original legend of zelda, adding in 'the old man' characters that gave you hints. the first dungeon in seasons (or was it ages? they're both so similar) is a remake of the dungeon in a tree (level 1 in LoZ). and the second dungeon in ages is a reamke of the second dungeon in link's awakening, even down to the same boss routine in a slightly different skin. a tribute to the first zelda in dungeon is fair enough, but there's no need to remake a dungeon that wasn't even that memorable from LA. the oracles just go too far in copying. however, to its credit, some of the later dungeons are pretty cool, simply because the oracles have access to 10 years of zelda puzzles to play around with.
however, oracle of ages does a nice job of continuing ocarina of time's concept, adding more change to the world (link can travel back into the past by 400 years). OoA feels quite a bit like crono trigger in this sense. but also, capcom have done a nice job of adding zany characters with little obscure and interesting lives (like 'vasu' who owns a house full of vases) which was always LA's strong point. there is also a trading quest that builds on link's awakening one, adding in some influence from MM.
epona is not the oracle games, but link's relationship with animals is furthered as an idea (and furthered even more in TP). link can now ride a lizard named dimitri, a bear called mooch and hop in the pouch of a kangaroo called ricky. it's charming of course, but like epona, they're simply ways of getting to places that link can't because he's too small or doesn't have wings.
the inventory of the oracle games borrows from nearly every zelda (giving old items new names such as 'harp of ages' = 'ocarina of time'). there is only one new item (as far as i recall), called the magnetic gloves. they are actually pretty cool and allow link to repel and attract himself using magnetic currents. i realized at this point that link is like james bond, or a child with a bunch of gadgets and toys to experiment with.
the storyline in the oracle games are beyond bad that it's just embaressing. i don't know if i even want to explain it all as it is convoluted beyond belief. something about 'general onox' the master of darkness that wants to bring the seasons of 'holodrum' into chaos (how will that make things dark exactly?). and how does he achieve this? he kidnaps the oracle of seasons who happens to be a pretty girl princess type. and somehow by doing that, the 'temple of seasons' collapses into the ground....and link as the chosen one must get the 'essences of nature' etc. etc.
the oracle games mark the point where zelda became a parody of itself, but also a celebration of its history. this extends to minish cap as well, which i don't really want to take up space talking about.