Just been through the Gamerankings lists for 3 of my 4 my consoles (I looked at Megadrive too but there were very few reviews and I didn't disagree with any scores I saw)
Games that fit your criteria (scored under 70% but I enjoyed them and think they should be higher)
N64
Destruction Derby 64 7.0 63.6%
Hydro Thunder 7.5 66.1%
Re-Volt 4.5 59.7%
South Park Rally 4.3 43.2%
V-Rally Edition '99 5.1 55.1%
(I wouldn't rate South Park Rally very highly, perhaps 60%, but I still enjoyed it)
Games that I think are very underrated, but still scored ok
N64
BattleTanx: Global Assault 7.6 76.0%
F-Zero X 8.1 86.1%
Jet Force Gemini 8.0 81.1%
Star Wars Episode I: Racer 7.1 75.8%
GameCube
Burnout 7.5 79.1%
Chibi-Robo 7.6 78.4%
Wii
Endless Ocean 8.7 74.3%
Excite Truck 8.5 75.4%
SSX Blur 7.8 74.4%
Wii Sports 8.5 76.5%
Zack & Wiki: Quest for Barbaros' Treasure 9.0 85.7%
Games that deserved the poor scores that they got.
Army Men: Sarge's Heroes 2 5.3 48.0%
Rugrats: Scavenger Hunt 3.3 52.7%
Wii Play 6.7 60.4%
(Wii play gets away with that score though, because the game is easily worth the £5/$10 you pay for it)
It seems all the ones that properly fit the question (in blue) are games I bought for the N64, likely because in those days I didn't check reviews at all, so I picked what looked good... that method obviously has it's flaws based on Army Men and Rugrats (and a couple of other N64 games that I wished I hadn't bought)
