As Gulgo has intimated there are a lot of varied views on the Ten so its probably fair to say its not perfect but at the price point it sits at its doing pretty damn good.
The Up/down sides in my view (as an ex ten owner - now S10)
suspension is cheap , underdamped and undersprung but does a good job at the same time ie I had no compliants about mine hooning on tarmac and it was only offroad that the stock units forced the pace to remain low, that in itself is probably a good thing for todays (UK) green lanes and the threat that they face from Nimbies etc.
Engine, its a unremarkable single that is neither powerful or slow and isnt super smooth nor does it vibrate badly. Some possibility for gearbox issues (mine had poor retention on 2nd gear) but could be rare.
body cheapish unpainted plastics but looks the part for a rugged adventure bike
footpegs - ****e swap em!.
oem Luggage , good if you dont expect them to act as tank armour/crash bars.

High speed, fast enough for uk m'way work but can be buffety (I notice this more now I have the S10 as it doesnt tire me as the Ten did).
Overall quality, not up to KTM stds but not bad and its not KTM prices either.

All just MO . Great bike for what it costs though and I think without many competitors , maybe the tiger XC800 is the nearest.

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ex XT660X Tenere, now XT1200Z Super Tenere