What do you like best?
1. The newest version of the Enterprise Edition supports a responsive framework. This is key in the growing mobile commerce trends. If you're not addressing responsive, you should, and you should strongly consider Magento because of it.
2. Magento is build on an attribution model. While this does require some getting used it...it's flexibility is far superior to any platform I've seen. Merchandisers and user experience designers will have a ball. Invest your time wisely in the planning process and you will reap the benefits in a stellar shopping experience with powerful search refinement
3. Magento is a complex beast of a shopping cart platform, but it has one of the largest communities and developer bases to boost. Play your cards right, and you'll enjoy an almost custom build-in house platform, for fractions of the cost.
4. Cache Management - We all hear the complaints about Magento's performance drag, but they've made great strides in the cache management and re-indexing capabilities. Add in an level of hole-punching features, coupled with a strong hosting partner, and you'll be praising the performance all the way to the bank.
5. Integration, Integration, Integration - With it's robust API, handsomely supported partner program, and easy to install extensions (use only trusted partners), finding a solution that you can't connect to is as easy as finding another planet with life...I'll keep my ears open.
What do you dislike?
1. Complex - Because of the way it's been marketed, many clients feel Magento is easy to use, right out of the box. I've built sites on Shopify and BigCommerce, two strong SaaS "out of the box" solutions. Magento is NOT one of them. With that said, it is incredibly robust, has an expansive developer community, and you have access to customize everything!
2. Performance - As mentioned, Magento is a resource hog, and without the skillful hand of an experienced system administrator, powerful hosting environment, clean code base (especially if your customizing), and thought out cache management solution, your site will covert as well as a geocities site in 2015.
3. Open Community - This is technically a big plus to Magento. Having a large open community is great, but it also lends itself to the creation of poorly written extensions and integration offerings. If you get sucked into the lure of cheaply priced (or free) extensions that promise the world, you'll experience the hurt from the havoc that they will have on your site. From extensions that override core template files (a huge no-no if you ever want to upgrade), to those that battle one another for supremacy, but result in a self imploded catastrophe, you'll need a knowledgeable partner to help you avoid these pitfalls.
4. Default Search - Default Magento on-site search functionality is terrible. Most clients will find a 3rd party solution. Luckily Magento has some great integration options with SOLR, SLI, and Celebros to name a few.
Recommendations to others considering the product
Make sure you work with a knowledgeable partner or technical resource when evaluating the platform or architecting your implementation. The right resource will make you love the switch, the wrong one will make you want to crawl in a hole to never hear the words Magento (or eCommerce) again.
What business problems are you solving with the product? What benefits have you realized?
I've been on both sides of the fence on this one. I've worked with Magento as an operator as well as a consultant...but the problems are the same... maximize profits through improved site visibility, on-site user experience, and functionality and streamlined operational processes.
I've used many platforms in the past, and while each has it's benefit, on the vein-diagram of features vs cost, vs scalability, Magento takes the cake.
I've seen vast improvements in SERP results through Magento's emphasis on SEO, increase in time on site, visits per page, conversation rates, and AOV by leveraging Magento's advanced out of the box attribute model to more naturally progress customers through the purchase funnel, and provide improved product up-sells and cross-sells.
If you're a mom and pop shop, Magento is robust enough to handle all your eCommerce needs, If you're more enterprise, it is a solid shopping platform with great product management and merchandising capabilities, while providing the ease in hooking into your existing operational eco-system.
The flexibility of Magento is killer. but make sure to have your King Arthur to wield the Excaliber sword that is Magento.