I play a lot of Medusa. I can't speak for the pro scene and what's going on there but I play her a lot in my pubs.

As someone adeptly pointed out, her itemization is unsolidified at the moment. Yasha is fantastic, but I don't like Manta even though the illusions get the split shot. She's a bit like Morphling, another stat hero, where one item is not enough. If you go tanky with Skadi, your damage sucks, if you go damage with a Demon Edge, you're squishy.

I personally like to play her mid and I like to go Bottle, Aquila, treads, Yasha, Point booster, maybe a demon edge and then a skadi. I actually tend to sell the Yasha in favour of other items, instead of finishing a Manta, if the game goes on long enough but usually it does not.

She's one of my go to heroes for a win. I think people underestimate what her ultimate can do to early game fights, if you land it at the right time and in the right place it can swing a fight completely. At the very least, the enemy cannot fight into it. She's also deceptively strong in teamfights because of Mystic Snake, it HURTS and it jumps to the backlines a lot where the supports commonly congregate and deals the most damage to them. A rank 4 Mystic Snake will do a substantial amount of damage on the last jump to an underleveled and underfarmed, low HP, int hero.

She's oddly well suited to the mid role because of her two skills. Mana shield and Mystic Snake. Mana shield makes her irritatingly hard to kill which is very popular in today's meta as a lot of people will attempt to gank mid. She's one of the few heroes that can sit in a lane with 2-3 enemy heroes occupying the opposing hill and farm. Albeit it's a little uncomfortable but it's not like an SF who is quite scared when he has 3 or so people looking at him with malcontent.

Mystic Snake is very good at pushing out the lane right before the rune spawn and can be very troublesome for some mid heroes to deal with as with a Bottle and an Aquilla, you can spam rank 3 or 4 fairly comfortable. With her tanky nature, it can be difficult for a support to run you down if they try and contest alone unlike other mid heroes who tend to be a bit squishy and can be bullied out of the river.

I've seen some pros skip Mystic Snake, Burning notably and I understand why. He was going for an AFK farm build. In my games I have gotten numerous kills from Mystic Snake getting a very long range finishing blow.

All that said however, she's not the type of hero that can drag her useless team along, she requires a little bit of space to be created for her. Not only so she can get dat gpm but in fights too as during the earlier stages of the game, she does not output a whole lot of damage unlike TA, SF, Luna, Slark etc.