I haven't written many reviews yet. Only two actually. But one was very negative and one was very positive. I wrote the negative one first, so my experience doesn't exactly fit this question. But for the record, I found writing both reviews to be about the same level of difficulty.
However... I do write book reviews for my friends sometimes, and strangely enough, I actually find it easier to write the negative reviews. When I dislike something, my brain really gets into figuring out exactly why I dislike it. But when I really like something, that part of my brain that does critical thinking (in both ways that phrase can be used) seems to just turn off. So I can be really specific about why I dislike something. But all I can say about something that I liked was "It's great! Really! It's great!" Which isn't very useful really.
I worried that I would have that problem when writing my very positive review for the Beaver. But I didn't. I was actually able to be very specific about why I loved it. Maybe because I've been using it for so many years.
But even when writing my review for the G Fun, which was no fun for me at all. I did find a way to say something positive about it. I'm of the belief that no matter how bad something is, you can usually find something positive to say about it. Don't lie. Just try to think about what someone else might actually like about it.