Here is product doc guide that expands on modules: Email Template Syntax - Marketo Docs - Product Documentation
Yes, it's possible to add more modules but you may need make edits in the email template itself and adhere to Marketo's email template syntax.
Jen, your best bet is to find an agency - or a self-service provider like Knak - and have the appropriate templates created for your specific use-cases. The ones that Marketo provides haven't been tested fully across all devices, clients (especially Outlook) and are quite limited/dated. Have a look at the all-in-one template that I posted in this discussion thread: Re: Moving off Marketo Designer
Adding to the great advice Dan provided above, Email Monks or Grazitti are also great options for fast turn around (and low prices). Both of those agencies are based in India and can turn templates around overnight for less than a couple hundred bucks each. They know Marketo 2.0 syntax really well. 10/10, would outsource again.
As a software developer, I agree completely with your opinion.
Marketo's interface is full of marketo specific syntax that is cumbersome and restricting. They have no error messaging, so you really have no ability to debug any error that pops up when attempting to build a template. This is maybe the worst CMS I have ever used.
If Marketo were classified in software development terms, it is a CMS, just like Wordpress or Drupal. It is designed for small mom and pop businesses that don't really have the ability to do marketing on their own. It lacks enterprise features or tools that allow for a great degree of customization.
But, I'll agree it is not a development tool.
Sorry to disagree, Marketo is not a CMS and has never claimed to be. It's a Marketing Automation / Lead management solution that happens to offer the possibility to create landing pages. In other terms, it's designed to manage leads, not content. Hence some limitations, shortcuts or lack of functionality.
I would call landing pages and email templates "content". It has tools for the composition of new content. It has an interface for viewing and managing data for large groups of people. It delivers content to users via email tools.
I don't think the criteria for a CMS is that it does these things well. Content management system - Wikipedia
Whether moonlighting as a CMS makes you a CMS or not is debatable, but for me, intent is not as important as functionality.
Marketo's interface is full of marketo specific syntax that is cumbersome and restricting
Marketo's proprietary syntax for LP and email templates provide the enhanced capabilities - like drag and drop modules to create unique email layouts via a single template - when those templates are properly designed/coded by those who are extremely familiar with Marketo template design and the custom syntax. For example, here's an all-in-one template that we use for all of our email communications:
It is designed for small mom and pop businesses that don't really have the ability to do marketing on their own.
Actually quite the opposite. Marketo's customers are SMB to enterprise businesses that have the appropriate staff (either in-house or by working with an agency/partner) to properly implement and customize the environment for the business (including integrating with CRM and other platforms that make up the tech stack - Marketo is often the core platform within the Marketing ecosystem). Tools like MailChimp, Constant Contact and Campaign Monitor, on the other hand, are geared toward the do-it-yourself types within a business. Here's a recent report that was published that describes in great detail the differences between the most popular platforms that make up the marketing automation landscape (ironically, if you look at the URL, you'll see that this report is served up through a Marketo instance):