I didn't care about 3D, it usually detracts from a film if anything, but IMAX is absolutely worth it when done right. There's no gimmickry behind IMAX like there is with 3D, it's just a recording format which means that the film has been recorded on significantly larger film (or, in the case of digital recordings, significantly larger sensor and resolution equipment), resulting in far greater visual quality, then played through a projector capable of articulating those visual improvements (audio is typically recorded and mastered to a higher fidelity too, and played through a better sound system). As a loose comparison, it's akin to moving from video recorded on your phone to professionally produced DSLR footage, or going from a 540p DVD through your TV's speakers to 4K BluRay and a high end hi-fi system. It's just a wholly improved viewing experience in general.
Interstellar and Mad Max Fury Road are my favourite examples of the benefits of the IMAX experience.
It doesn't make sense for everything though. Greater resolution doesn't matter for romcoms for example, and a poorly produced film could potentially even get worse if they attempt to artificially upscale to IMAX quality during editing. Most importantly a bad film is a bad film and a good film is a good film regardless of format- IMAX can't save a bad film, it can only enhance a good one!