Yeah, even for somewhat "inexperienced RPG players", I think all of 3-7 are still worth a try.
In my book 3-5 actually aged a bit better than 6-7 in terms of visuals.
3D from 90´s is generally a visual representation type that belongs among the most prone to aging (and I think M&M´s felt somewhat obsolete even at the release dates), the colour scheme and empty corridors make for a pretty bland visual experience and 2D models add an ever present element of inconsistency. 3-5´s 2D may be sorta childish, but it´s consistent and better defined.
Among the 3-7, for "inexperienced RPG players", I would recommend 4+5 combo (World of Xeen) and 7 the most. IIRC, World of Xeen features a bit more convenient UI, slightly less difficult puzzle element and I remember 5 as the best of these 3 overall.
Compared to 6, IIRC 7 also has at least one feature improving convenience (markers on already visited houses, which cuts the time spent on looking for trainers) and it´s not as difficult overall. It also has more interesting character development (probably best in the series), major choice in the middle and a cool minigame. 6 has more memorable dungeons, bigger environmental diversity and better ending, but it also features elements which someone may find detracting - personally I´ve found the amount of enemies to be overkill and a lot of dungeons to be way too long for their own good - I´ve actually found these two aspects so annoying that it put 6 at my least favourite spot of the 3-7 bunch. Tomb of Varn and Darkmoor Castle rule though
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