One way you could keep games 'fresh' and 'exciting' is with different types of Jungle creeps.
The difference would only be visual and players would have the option to turn it on/off in the client.
Think of it like skins for Jungle creeps (excluding the buffs and epic monsters). Some could be regular, some rarer, some seasonal. Some could have special requirements, like there's >3 Freljordian Champs on the team so you get a Snowman, or >3 Shuriman Champs so you get a cactus-hound-monster, or >3 Water-y champions so you get a floating Pufferfish.
I remember there were a bunch of unused monster concepts when you did the Summoner's Rift Update. You could reuse those or bring back Lizards and Wraiths. The Slimes could be a nice replacement for the new Krugs. You could have a baby Vilemaw to replace Gromp and the removed buff helpers (the masked bushes and floating stones) for Wolves and Raptors.
Seeing different visual aspects every game could keep things from feeling static, and it would be healthier for balance than revamping the Jungle every season.
visual updates