What do you like best?
It has nearly everything I need.
Check out this screenshot: https://www.dropbox.com/s/fb90rz6hbrbmu99/Screenshot%202014-07-11%2011.56.21.png
They just rolled out Premium and it's only $19 per month to begin, which is pretty awesome.
It connects with the major email marketing tools, some SEO tools, most social networks (they were one of the first to connect with Google+), and tons of great ecommerce applications. This means you can measure an (estimated) sales funnel - or at the very least track corrolary spikes/dips in traffic, and see which social network(s)/email campaign(s)/landing pages are affecting what sales/traffic. I doubt there is a better analytics platform in existence for ecommerce.
It also connects with Bing Ads and Google Adwords.
What do you dislike?
Still missing integration with LinkedIn (not even company pages or profiles). They've said this is because LinkedIn's stupid API does this refresh thing every month that basically kicks out anyone connected to it (in Hootsuite, for example, you have to reconnect your LinkedIn accounts every month). But it's unfortunate to have such vast capabilities... without LinkedIn.
Also, sometimes the platform can be a little glitchy. This was more true back when they were just getting launched. I've used Sumall since mid 2013. While it IS getting smoother, there are random periods of missing data every once in a while... which makes reporting to clients very difficult. I usually just export the data and give my best guess for a filler.
Also, they DESPERATELY need to enable grouping of accounts. They've told me this is in the roadmap for premium users, but it's not there yet, so connecting a lot of accounts turns it into a mess.
They also need to make it so you can reorder accounts in the left sidebar panel.
Recommendations to others considering the product
Your data for most data points accumulates once you've connected - so go and get connected right away! Then let the data gather for a week or so, and prepare to be amazed.
What business problems are you solving with the product? What benefits have you realized?
Ecommerce has long needed a solution like this. For social marketing - my primary use - it displays how social integrates with other content/digital marketing efforts (email, web traffic, paid search, etc), which is incredibly valuable to report to higher-ups and also to clients.