Things you do right
1) 140kg is not bad
2) Back was mostly straight. Not totally, but you know what you messed up on, and you'll probably fix it without other people ragging on you for it.
3) You're facing forward during the lift. Solid. Should help back alignment.
4) Using a mixed grip without straps. Good.
Things you could do more right
1) Don't wear long pants when you deadlift. The crease at the waist makes the pants ride up which decreases the slack in the sleeve around your knee which prevents it from moving forward. Your leg doesn't move forward MUCH in the deadlift, but in getting proper mechanical position, it's gotta move SOME. Your pants are preventing them from doing that. Buy some athletic shwag.
2) Hump the bar when you're at the top. Rotating your pelvis forward does some magic that I've never been able to remember for more than five minutes at a time, but I think it has something to do with removing tension from your lower back/getting full ROM/looking as awesome as a T-Rex with a rocket launcher reading Faulkner.
3) Ditch the belt. When beginners use belts, it means they've got both a hernia and brain damage, or a vagina. You've (most likely) got neither. Ditch it. Your abs are strong enough to support a 140kg dl, and if they're not, they should be.
FWIW, I don't think the bar has to come to a complete stop at the end of every rep, you won't destroy your back by descending slowly and under control in the DL, setting it up in a rack is a good idea because you get to gauge how heavy the weight feels on the eccentric, not the concentric portion of the exercise, so you're stronger and at less risk of injury/stupidity, and you're not that shitty a dl-er for the beginner section. I was around when deisel_weasel was posting. That man took fourteen pages of solid flaming to realize he MIGHT have a problem with DL form. And HE was doing it with +400#, IIRC.