The negatives are
- Costly, but if you are using it over air then it's not so bad
- Very easy to bait into firing
- Long reload time
- Needs a lot of micro to make it cost effective
- Terrible for holding pads
- Hard to get cards
The biggest negative for me though is that it becomes utterly useless if there's a level difference meaning it won't one shot what you need it to. I played big boss, recognised the name and went try hard to try and harpoon the biggest of whales. Got the the first missile and was very close to the second before he rolled out artillery, I couldn't one shot them so I then got destroyed because it bought him enough time to defend and roll out more. If they died in one volley I think I would have won despite his lvl 13-15 units and my 9-10.
But the pros are pretty obvious, it's fast, can one shot most air units (not the kodiak or I think basilisk too) and is very versatile and imo is better than the phantom in almost every deck. It's perfect for defending something like a giga cannon or taking out harvesters.
Definitely something I always want in my deck but if like me you rely on it and don't use air then you're very vulnerable to many units so it's not a perfect replacement.