I thought I may as well leave my last impression of Invel here, feel free to tell me why you disagree with what I think etc. :P
So Invel, I found him to be a tiny bit intriguing at first, being Zeref's right hand man and all, and his demeanor was definitely one of a secretary of sorts to me, at least. As the Alvarez arc went on, Invel was held from the fray for a fair while hence which is why I started really feeling some hype for his fight as I thought unlike a lot of the other spriggan he would really have some impact, and that he did with Juvia "dying", just for one chapter.
As for his actual fight with Gray, I enjoyed it at first, it had a good flow and had me interested in what would happen next, which Ice vs Ice fights don't usually do for me these days. What let me down with Invel combat-wise was how he lost to Gray, he simply got blown away by PoF and Nakama power, which was really disappointing for a character I'd been enjoying this far. and it was a rather underwhelming end to the fight imo, and it tarnished him a tiny bit as a character.
So, Invel started out as a good character who gained hype as things went along and I really hoped we'd see something big and impactful from him, but in the end all we got was the E.N.D reveal (which was alright), a fake death and him getting overpowered by the Power of Friendship. A bit disappointing if I do say so myself.